Method for acoustic information exchange involving an ingestible low power capsule

ABSTRACT

A method of communicating with an ingestible capsule includes detecting the location of the ingestible capsule, focusing a multi-sensor acoustic array on the ingestible capsule, and communicating an acoustic information exchange with the ingestible capsule via the multi-sensor acoustic array. The ingestible capsule includes a sensor that receives a stimulus inside the gastrointestinal tract of an animal, a bidirectional acoustic information communications module that transmits an acoustic information signal containing information from the sensor, and an acoustically transmissive encapsulation that substantially encloses the sensor and communications module, wherein the acoustically transmissive encapsulation is of ingestible size. The multi-sensor array includes a plurality of acoustic transducers that receive an acoustic signal from a movable device, and a plurality of delays, wherein each delay is coupled to a corresponding acoustic transducer. Each delay may be adjusted according to a phase of a signal received by the corresponding acoustic transducer.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims the benefit of U.S. Provisional PatentAppl. No. 60/842,360, filed Sep. 6, 2006, and U.S. Provisional PatentAppl. No. 60/941,184, filed May 31, 2007, each of which is incorporatedby reference herein in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to medical device communication,and in particular, to communication with ingestible medical diagnosticdevices.

2. Background Art

The population of the United States is aging. The first wave of the 78million “Baby Boomers” is beginning to turn 60 years old. Coincidingwith this aging of population is a rising concern regarding the publichealth, and a generally more educated patient in technology awareness.There has been an explosion in diabetes cases, estimated at 194 millioncases worldwide today, and predicted to be 350 million cases by year2025. Obesity currently affects two thirds of the U.S. population. Thereis a rising incidence of cardiac problems for women (the #1 cause ofdeath for women). Hepatitis C will soon reach epidemic levels, infectingnearly 5 million people, more than the number of approximately 1.2million people infected with HIV/AIDS in the U.S. Celiac disease affectsapproximately 2.2 million people in the U.S., with about 97% beingundiagnosed. The prevalence of further serious conditions, such as coloncancer, other cancers, ultra- or ulcerative-colitis, lactoseintolerance, allergies, irritable bowel syndrome, Crohn's disease, etc.,indicate that there is a need for simple and easy diagnostic techniques,especially because many of these diseases are chronic, requiring repeattesting over time. Some conditions, such as cancer, are most responsiveto treatment if caught in the early stages. Cancer, for example, is bestdetected in the digestive tract. Given that cancerous growth can occurin as little as one to two years, it is essential to detect cancer orcancerous precursors at least annually, or preferably biannually.Physician and health care resources are currently already stretched andwill fail if the current technology, process and procedure are notaltered to suit the needs of the baby boomer market of the near future.Time-saving and simple solutions to diagnostics are needed.

The current population desires speedy testing and fast answers to theirhealth questions. Many current testing and monitoring systems arelimited by old technology and processes that take days, if not weeks,for results. These test methods, if not inconvenient and potentiallyembarrassing, are at least in most cases intrinsically painful or riskyto patients.

One ingestible diagnostic device in the market today is a disposable RFcamera pill or capsule camera, which captures images of thegastro-intestinal (GI) tract as it passes through. Current camera pillusage by patients and physicians is limited in many different ways.First and foremost, the current technology is very large in comparisonto most ingestible medicines and nutritional supplements. The excessivesize is in large part a result of the selection of power-inefficientcommunication methods. The large size mandates pre-screening of patients(an additional process, inconvenience, and cost). The large size alsoleads to a reasonably high potential that the device can become lodgedwithin the GI tract. This may lead to a highly invasive surgical removalrequirement, which carries all the risks associated with surgeries.

Additionally, the current camera pill systems require a bulky readingdevice worn as a belt around the waist and adhesive sensors attached tothe body to capture the electromagnetically-coupled signal sent from thepill. The patient is required to report to a physician's office forprescreening, to initiate use of the camera pill, and to be fitted withthe belt reader. The belt reader is worn for 24 hours, during which timethe camera pill captures images and transmits the images via radiofrequencies (RF) to the belt reader. At the end of a diagnosis period,the patient (and belt reader) must return to the physician. Thephysician is first required to download images from the belt reader andthe analyze the images. The physician may analyze the images and discussthe results with the patient at yet another appointment during asubsequent visit. Thus, current camera pills require three, four, ormore trips to the physician's office, as well as the wearing of acumbersome belt reader with leads attached to the skin.

This diagnostic process is both inconvenient and uncomfortable. It alsocarries a risk of surgical removal, due to the size of the currentcamera pills. Current technology does not offer a recorded positionwithin the body associated to the specific image taken. Physicians mustachieve a location of an image of interest through yet anotherprocedure. Furthermore, the current camera pills are expensive devices,and are resorted to when other bowel disease diagnostic techniques, suchas endoscopy and colonoscopy (each of which are extremely intrusive),present results that need further investigation. Further, theelectromagnetic signals used to transmit the images may harm thesensitive tissue they pass through in order to be detected outside thebody. Therefore, the current ingestible camera pill has significantdeficiencies.

What is needed are diagnostic devices, services and processes that areconvenient, simple, relatively inexpensive, comfortable, take less time,directly detect specific compounds or indicators to disease, and havemore applications.

BRIEF SUMMARY OF THE INVENTION

A method of communicating with an ingestible capsule includes detectingthe location of the ingestible capsule, optionally focusing a detector(which may be a single sensor or a multi-sensor acoustic array) on theingestible capsule, and communicating an acoustic information exchangewith the ingestible capsule via the detector. The ingestible capsuleincludes a sensor that receives a stimulus inside the gastrointestinaltract of an animal (e.g., a human), an acoustic informationcommunications module that transmits an acoustic information signalcontaining information from the sensor, and an acoustically transmissiveencapsulation that substantially encloses the sensor and communicationsmodule, wherein the acoustically transmissive encapsulation is ofingestible size and material.

The ingestible capsule can transmit information by applying one or morebase voltages to an electromechanical transducer or piezoelectric (e.g.,PZT, PVDF, etc.) device to cause the piezoelectric device to ring atparticular frequencies, resulting in an acoustic transmission. Amulti-sensor array for receiving the acoustic transmission may include aplurality of acoustic transducers that receive the acoustic transmissionfrom a movable device such as an ingestible capsule.

These and other advantages and features will become readily apparent inview of the following detailed description of the invention. Note thatthe Summary and Abstract sections may set forth one or more, but not allexemplary embodiments of the present invention as contemplated by theinventor(s).

BRIEF DESCRIPTION OF THE DRAWINGS/FIGURES

The accompanying drawings, which are incorporated herein and form a partof the specification, illustrate the present invention and, togetherwith the description, further serve to explain the principles of theinvention and to enable a person skilled in the pertinent art to makeand use the invention.

FIG. 1 illustrates a partial view of a human according to an embodimentof the present invention.

FIG. 2 is a block diagram of an ingestible capsule according to anembodiment of the present invention.

FIG. 3 is a block diagram of a communications module according to anembodiment of the present invention.

FIG. 4 is a block diagram of an ingestible capsule according to anotherembodiment of the present invention.

FIG. 5 is a block diagram of a communications network according to anembodiment of the present invention.

FIG. 6 is a block diagram of an exemplary communications networkutilizing a sensor link module according to an embodiment of the presentinvention.

FIG. 7 is a block diagram of a sensor link module according to anembodiment of the present invention.

FIG. 8 is an exemplary computer system useful for implementing thepresent invention.

FIG. 9 is a block diagram of an ingestible capsule according to yetanother embodiment of the present invention.

FIG. 10 is a circuit diagram of an acoustic communications moduleaccording to an embodiment of the present invention.

FIG. 11 is a cross-section of a piezoelectric transducer according to anembodiment of the present invention.

FIG. 12 is an exemplary step function.

FIG. 13 is another exemplary step function.

FIG. 14 is a block diagram of a phased array according to an embodimentof the present invention.

FIG. 15 is an illustration of an acoustic biobus according to anembodiment of the present invention.

FIG. 16 illustrates a power source for an acoustic transmitter accordingto an embodiment of the present invention.

FIG. 17 illustrates a block diagram of an acoustic data transmissionsystem utilizing a spreading code according to an embodiment of thepresent invention.

FIG. 18 illustrates a block diagram of an acoustic transmitter thatutilizes a phase shift keying (PSK) modulation scheme and a spreadingcode according to an embodiment of the present invention.

FIG. 19 illustrates a block diagram of an acoustic receiver of anacoustic data transmission system that utilizes a PSK modulation schemeand a spreading code according to embodiments of the present invention.

FIG. 20 illustrates a block diagram of a transmitter of an acoustic datatransmission system that utilizes a differential PSK (DPSK) modulationscheme and a Barker spreading code according to an embodiment of thepresent invention.

FIG. 21 illustrates a block diagram of a receiver of an acoustic datatransmission system that utilizes a DPSK modulation scheme and a Barkerspreading code according to an embodiment of the present invention.

FIG. 22 illustrates a block diagram of a transmitter of an acoustic datatransmission system that utilizes a DPSK modulation scheme and a Barkerspreading code according to another embodiment of the present invention.

FIG. 23 illustrates a block diagram of a receiver of an acoustic datatransmission system that utilizes a DPSK modulation scheme and a Barkerspreading code according to another embodiment of the present invention.

FIG. 24 illustrates a block diagram of a receiver of an acoustic datatransmission system that extracts a signal from a plurality of reflectedsignals according to an embodiment of the present invention.

FIG. 25 illustrates a block diagram of a transmitter of an acoustictransmission system that uses two types of DPSK modulation according toan embodiment of the present invention.

FIG. 26 illustrates a block diagram of a receiver of an acoustictransmission system that uses two types of DPSK modulation according toan embodiment of the present invention.

FIG. 27 illustrates a frequency hopping (FH) scheme to encode and/ordecode an acoustic communication signal according to an exemplaryembodiment of the present invention.

FIG. 28 illustrates a hopping pattern used to encode and/or decode theacoustic communication signal according to an exemplary embodiment ofthe present invention.

FIG. 29A illustrates a combined FH and pulse interval encoding (PIE)scheme to encode and/or decode an acoustic communication signalaccording to an exemplary embodiment of the present invention.

FIG. 29B further illustrates the combined FH and PIE scheme according toan exemplary embodiment of the present invention.

FIG. 30A illustrates a combined FH and differential phase shift keying(DPSK) scheme to encode and/or decode an acoustic communication signalaccording to an exemplary embodiment of the present invention.

FIG. 30B further illustrates the combined FH and DPSK scheme accordingto an exemplary embodiment of the present invention.

FIG. 31 illustrates a block diagram of a transmitter to encode aninformation signal using a combined FH and DPSK scheme according to anexemplary embodiment of the present invention.

FIG. 32 illustrates a block diagram of a receiver to decode an acousticcommunication signal using a combined FH and DPSK scheme according to anexemplary embodiment of the present invention.

FIG. 33A illustrates a hopping pattern used to encode and/or decode anacoustic communication signal using a combination of FH and differentialfrequency shift keying (DFSK) according to an exemplary embodiment ofthe present invention.

FIG. 33B further illustrates the hopping pattern used to encode and/ordecode the acoustic communication signal using the combination of FH andDFSK according to an exemplary embodiment of the present invention.

FIG. 33C illustrates a combined FH and DFSK scheme to encode and/ordecode an acoustic communication signal according to an exemplaryembodiment of the present invention.

FIG. 34A illustrates a combined FH, DFSK, and DPSK scheme to encodeand/or decode an acoustic communication signal according to an exemplaryembodiment of the present invention.

FIG. 34B further illustrates the combined FH, DFSK, and DPSK schemeaccording to an exemplary embodiment of the present invention.

FIG. 34C further illustrates the combined FH, DFSK, and DPSK schemeaccording to an exemplary embodiment of the present invention.

FIG. 35 illustrates a block diagram of a transmitter to encode aninformation signal to a combination of FH, DFSK and DPSK acousticcommunication signal according to an exemplary embodiment of the presentinvention.

FIG. 36 illustrates a block diagram of a receiver to decode aninformation signal from an acoustic communication signal encoded using acombination of FH, DFSK and DPSK according to an exemplary embodiment ofthe present invention.

FIG. 37 illustrates a block diagram of a demodulator to decode aninformation signal from an acoustic communication signal encoded using acombination of FH, DFSK, and DPSK according to an exemplary embodimentof the present invention.

FIG. 38 illustrates a block diagram of a demodulator to decode aninformation signal from an acoustic communication signal encoded using acombination of FH, DFSK, and DPSK according to another exemplaryembodiment of the present invention.

FIG. 39A illustrates a hopping pattern used to encode and/or decode anacoustic communication signal using multiple frequency bands with FHaccording to an exemplary embodiment of the present invention.

FIG. 39B illustrates a multiple frequency band with FH scheme to encodeand/or decode an acoustic communication signal according to an exemplaryembodiment of the present invention.

FIG. 39C illustrates a multiple frequency band with FH and time intervalencoding scheme to encode and/or decode an acoustic communication signalaccording to an exemplary embodiment of the present invention.

FIG. 39D illustrates an advancement function that may be used with themultiple frequency bands with FH and time interval encoding schemeaccording to an exemplary embodiment of the present invention.

The present invention will now be described with reference to theaccompanying drawings. In the drawings, like reference numbers indicateidentical or functionally similar elements. Additionally, the left-mostdigit(s) of a reference number identifies the drawing in which thereference number first appears.

DETAILED DESCRIPTION OF THE INVENTION I. Introduction

Methods, systems, and apparatuses for ingestible capsules are described.Furthermore, methods, systems, and apparatuses for operating andcommunicating with the ingestible capsules are also described. Thepresent specification discloses one or more embodiments that incorporatethe features of the invention. The disclosed embodiment(s) merelyexemplify the invention. The scope of the invention is not limited tothe disclosed embodiment(s). The invention is defined by the claimsappended hereto.

References in the specification to “one embodiment,” “an embodiment,”“an example embodiment,” etc., indicate that the embodiment describedmay include a particular feature, structure, or characteristic, butevery embodiment may not necessarily include the particular feature,structure, or characteristic. Moreover, such phrases are not necessarilyreferring to the same embodiment. Further, when a particular feature,structure, or characteristic is described in connection with anembodiment, it is submitted that it is within the knowledge of oneskilled in the art to effect such feature, structure, or characteristicin connection with other embodiments whether or not explicitlydescribed.

Furthermore, it should be understood that spatial descriptions (e.g.,“above,” “below,” “up,” “left,” “right,” “down,” “top,” “bottom,”“vertical,” “horizontal,” etc.) used herein are for purposes ofillustration only, and that practical implementations of the structuresdescribed herein can be spatially arranged in any orientation or manner.Likewise, particular bit values of “0” or “1” (and representativevoltage values) are used in illustrative examples provided herein torepresent information for purposes of illustration only. Informationdescribed herein can be represented by either bit value (and byalternative voltage values), and embodiments described herein can beconfigured to operate on either bit value (and any representativevoltage value), as would be understood by persons skilled in therelevant art(s).

The example embodiments described herein are provided for illustrativepurposes, and are not limiting. Further structural and operationalembodiments, including modifications/alterations, will become apparentto persons skilled in the relevant art(s) from the teachings herein.

Methods and systems for an ingestible capsule are described. Theingestible capsule may be swallowed by an animal to diagnose or aid inthe diagnosis of one or more conditions of the animal through either animmediate detection or a historical and/or statistical analysis ofmultiple detections of conditions or attributes over a time period.Example embodiments are described below as related to a human subject,for illustrative purposes. However, embodiments of the present inventionare applicable to further types of animals other than humans, includinglivestock (cattle, sheep, pigs, chickens, turkeys, ostriches, etc.),pets (e.g., dogs, cats, horses, etc.), and other animals of interestsuch as race horses or other performance/sport animals. Suchapplicability to these types of animals, and other types, will beapparent to persons skilled in the relevant art(s) from the teachingsherein, and is within the scope and spirit of embodiments of the presentinvention.

Furthermore, example embodiments are described below as related topassing an ingestible capsule through a gastrointestinal tract, forillustrative purposes. However, embodiments of the present invention areapplicable to further bodily systems other than the gastrointestinaltract, including the circulatory system, the urinary tract, and otherbodily systems and additionally other means of entry or implant into abody cavity of an animal or human. Such applicability to other types ofbodily systems will be apparent to persons skilled in the relevantart(s) from the teachings herein, and is within the scope and spirit ofembodiments of the present invention.

II. Ingestible Acoustic Device

FIG. 1 shows a partial view of a human 102 according to an embodiment ofthe present invention. In FIG. 1, human 102 has swallowed or ingested aningestible capsule 104. Ingestible capsule 104 is configured to senseone or more attributes or conditions of human 102 as ingestible capsule104 passes through human 102. While passing through human 102,ingestible capsule 104 transmits information in a communication signal106 to be received on the outside of the human 102. Ingestible capsule104 may send information to and receive information from an externaldevice, or it may be a beacon that only emits information to theexternal device. As shown in FIG. 1, an external computing device 108may receive communication signal 106. Computing device 108 may be usedto display the information received in communication signal 106, tointeract with the information, to process the information, and/or totransmit the information (raw or processed) to another entity orcomponent. In an embodiment, computing device 108 can interact withingestible capsule 104 to control functions of ingestible capsule 104.

In a simplistic embodiment, computing device 108 may simply act as aprotocol converter in a store and forward manner. However, in a morecomplex environment, computing device 108 may perform complex andintensive functions such as data normalization, compression, andencryption for example.

In another advanced embodiment, computing device 108 can interact withingestible sensor device 104 to control functions of ingestible sensordevice 104. This embodiment infers a bidirectional communication 106with sensor device 104. Bi-directional communications are generallycommon place with persons skilled in the art. However, these designs aretypically designed to be able to receive signals either at times nottransmitting, or at all times. These common techniques are not desirablein the described environment as receivers require power, and additionalpower would consequently add to the size of sensor device 104. Externalcomputing device 108 receives and stores commands and/or informationfrom a network. Upon termination of the next transmission from sensordevice 104, sensor device 104 may turn on a receiver for a very shortamount of time, while external device 108 commences transmission ofcommands or information to sensor device 104. Greatly reduced powerrequirements on sensor device 104 are gained from very rapidly turningoff a receiver when no communications (or an indication of noinformation to communicate) are received from device 108 within adefined time window after a last transmission from sensor device 104.

In embodiments, human 102 may be provided with one or more ingestiblecapsules 104 that human 102 may at designated times and/or periodicallyswallow to perform an analysis of one or more health-related conditionsof human 102. Multiple ingestible capsules 104 may interact with device108 and/or each other. An exemplary ingestible capsule is described inco-pending U.S. Patent Appl. Ser. No. 11/851,221, titled “Ingestible LowPower Sensor Device and System for Communicating with Same,” which isincorporated by reference herein in its entirety.

FIG. 2 shows an example block diagram of ingestible capsule 104,according to an embodiment of the present invention. In FIG. 2,ingestible capsule 104 includes an acoustically transmissiveencapsulation 208 that holds one or more sensors 202, a communicationsmodule 204, and a power source 206. Although FIG. 2 illustratesingestible capsule 104 as having three sensors 202 a, 202 b, and 202 c,one of skill in the art will recognize that any number of sensors may beincluded in ingestible capsule 104. In one embodiment, there may be nosensor(s) 202 at all, providing a capability to track the pill movementin space, hence allowing a mapping of a gastro-intestinal tract and alsothe time of movement within that tract.

In an embodiment where ingestible capsule 104 has one or more sensor(s)202, sensor(s) 202 are used to sense (e.g., measure, detect, etc.) areceived stimulus 210, and generate a sensor output signal 212. Sensoroutput signal 212 may be a digital or analog signal, depending on theparticular implementation of sensor 202. In alternative embodiments theacoustically transmissive encapsulation 208 may be made of sensor(s)202, or sensor 202 may be integrated within the materials known asacoustically transmissive encapsulation 208. Ingestible capsule 104 caninclude any number of sensors 202, each of which may all sense the samecondition or may sense a different condition than another sensor 202.Sensor 202 may detect and/or interact directly with conditions of thebody. Sensor 202 may also detect and/or interact with signals emanatingfrom the pill and reflecting off nearby tissues, such as is the casewith, for example and without limitation, a camera detecting light thatoriginates from the capsule, ultrasonic detectors, and radioactivitysensors. In an embodiment, sensor 202 detects reflections of signal 106from nearby gastro-intestinal and other body tissues.

Logic control 214 initiates activity of sensor 202. Sensor 202 detectsor interacts with the body via signal 210 and produces a sensor outputsignal 212. Communications module 204 receives sensor output signal 212,and generates communication signal 106 to include information based onsensor output signal 212. Communication signal 106 is transmitted fromingestible capsule 104.

In an example embodiment, as shown in FIG. 3, communications module 204may include an acoustic communications module 302, configured totransmit and/or receive an acoustic communications signal. For example,acoustic communications module 302 may include one or more acoustictransducers. Sensor output signal 212 is modulated on an acoustic signalthat is transmitted as communications signal 106 by the acoustictransducer(s). The acoustic communications signal 106 may be transmittedby radiating element 304, which may be, for example, anelectromechanical transducer or piezoelectric (e.g., PZT, PVDF, etc.)element or transducer that vibrates at acoustic or ultrasonicfrequencies. An example acoustic frequency range in which acousticcommunication signal 106 may be transmitted is 20 Hz to 16 KHz, althoughthe frequency may be an acoustic frequency higher or lower than thisrange in some applications. An example frequency for acousticcommunications signal 106 is 40 Hz. In another example embodiment,acoustic communications module 302 may include an ultrasoniccommunications module, configured to transmit and/or receive acommunications signal at ultrasonic frequencies (e.g., between 0.5 to 5MHz). Generally, transducers are smaller for ultrasonic frequencies,which is useful for a very small sensor device. However, smaller devicesalso generally transmit less power through a medium and thus need tohave a high power input and hence a larger battery. Higher frequencytransducers do generally have a higher bandwidth and may have an impacton the amount of sensor data can be transmitted to a receiver. However,attenuation is greater for higher frequencies. A person skilled in theart of acoustic transducers will be able to select an appropriatefrequency range for an ideal situation of size and power consumption.

Communications module 204 may be configured to modulate information ofsensor output signal 212 according to a variety of modulationtechniques, including amplitude modulation (AM), frequency modulation(FM), and phase modulation (PM), and including any combination of thesemodulation techniques, including in quadrature or other modulationschemes. Acoustic pressures according to embodiments may have variouslevels, including greater or lower than 1 Pa, including in the KPa (orgreater) range to the μPa (or less) range.

FIG. 4 shows a view of ingestible capsule 104, with communicationsmodule 204 including acoustic communications module 302. In FIG. 4,communications module 204 is coupled to acoustically transmissiveencapsulation 208. Acoustically transmissive encapsulation 208 vibratesaccording to acoustic communications module 302 to transmit acommunications signal 402, which is an acoustic version ofcommunications signal 106. In FIG. 4, acoustically transmissiveencapsulation 208 functions as an acoustic radiating element, vibratingat acoustic frequencies according to acoustic communications module 302.

Returning to FIG. 2, operation of ingestible capsule 104 may be gatedand controlled by control logic 214, which itself may be operating in asub-threshold voltage (Vt) manner (e.g., to save power), or controllogic 214 may operate in normal bias modes. In an embodiment, ingestiblecapsule 104 is an autonomous device with one way communication(transmission capability), so that control logic 214 may be extremelysimple, and thus would not consume much power even when operating innormal bias modes. However, in another embodiment, ingestible capsule104 may communicate in both directions, and may be configured to receiveinstructions from computing device 108. Control logic 214 may thus haveadditional complexity in order to, for example, decode and implementreceived instructions.

Power source 206 provides power (e.g., via electrical energy) to operatethe components of ingestible capsule 104 that require power, such ascommunications module 204 and/or sensor 202. Power source 206 mayinclude, for example and without limitation, a battery, a liquid, or anenergy harvesting module.

In an embodiment, power source 206 includes a liquid or semi-liquid,such as is illustrated in FIG. 16. In this embodiment, communicationssignal 106 is a signal of acoustic nature, and power source 206 includesan electrolyte 1601 in the form of an acoustically transmissive materialsuch as a liquid or semi-liquid. Electrolyte 1601 serves a first purposeof a battery component but also serves an efficient medium of acoustictransmission. Furthermore, as illustrated in FIG. 16, a material 1602serves a dual purpose of housing battery 1601 as well as othercomponents, while allowing an efficient transfer of acoustic energy frominside to outside of ingestible capsule 104. FIG. 16 additionallydemonstrates control and regulation component 206 a, anode 206 b, andcathode 206 c.

Communication signals 106 pass through electrolyte 1601 and externalanimal flesh environment 1603. In the case of an acoustic propagation,the most efficient energy transfer is accomplished when the acousticmaterial impedance from material to material is gradually changed fromorigin to destination from high to low, or low to high impedance as iscommon knowledge to those skilled in the art. Communication signal 106then is demonstrated in FIG. 16 as a combination of signals 106 a and106 b to illustrate the change in medium properties from electrolyte1601 through housing material 1602 and into flesh 1603. As one exampleof many, electrolyte 1601 may be a citric juice or gel that isnon-harmful to human consumption; anode 206 b and cathode 206 c mayinclude zinc and copper, which is also not harmful to human consumption;and housing 1602 may be comprised of a thin but soft plastic ofreasonable acoustic impedance to electrolyte 1601 and animal flesh 1603.However, other material selections by those skilled in the art ofbattery technology and acoustic propagation for electrolyte 1601,housing 1602, anode 206 b and cathode 206 c do not depart from thespirit of this invention.

In an embodiment, ingestible capsule 104 is configured for low poweroperation, including extreme low power (XLP) operation. To achieve XLPoperation, ingestible capsule 104 can use one or both of a very smallbattery and energy harvesting to operate ingestible capsule 104. In anembodiment, circuits of ingestible capsule 104 are implemented in one ormore integrated circuits (ICs), in a technology such as CMOS, or othertechnology. The IC(s) and any other internal components of ingestiblecapsule 104 may be mounted to a circuit board, or mounted directly toacoustically transmissive encapsulation 208. Thus, in embodiments, powersource 206 is configured for low power output, including supplying powerin the milliwatt and microwatt ranges. Such low power requirementsenable the size of power source 206 to be minimal.

In a CMOS embodiment, MOSFET circuits may be configured to operate in adeep sub-threshold voltage (sub-Vt) mode, which lowers their switchingtime to acoustic switching frequencies, and lowers their powerconsumption by orders of magnitude. In such a mode the MOSFET devicesoperate as analog devices. Such operation was demonstrated in themid-1980's by Carver Meade with regard to eye and ear chips. Such a modeof operation eliminates the need for digitizing the sensor information,which can be very power intensive, and which further reduces the powerconsumption by a large factor. Further details on such sub-thresholdvoltage MOSFET circuits may be found in the following U.S. Patents,which are incorporated herein by reference in their entirety: U.S. Pat.Nos. 6,198,324, 6,252,448, 6,297,668, and 6,333,656.

Acoustically transmissive encapsulation 208 contains sensor 202,communications module 204, and power source 206, and is configured to beingestible by or inserted within a human and/or animal. Acousticallytransmissive encapsulation 208 may be the size of a vitamin or othertype of pill that is ingestible by humans. For example, acousticallytransmissive encapsulation 208 may be approximately 3 mm in diameter andapproximately 5 mm in length. Acoustically transmissive encapsulation208 may be any suitable shape, including oval, elliptical (as shown inFIG. 2), capsule shaped, or spherical. The small size of acousticallytransmissive encapsulation 208 allows ingestible capsule 104 to beeasily ingested by an average human 102. The small size overcomesdifficulties present with existing camera pills, which are often solarge that only a small percentage of the population can actuallyswallow them. Further, the small size of acoustically transmissiveencapsulation 208 increases the ability of ingestible capsule 104 topass completely through the digestive system of a human 102 withoutbecoming trapped due to size incompatibility.

Acoustically transmissive encapsulation 208 may be made from a varietyof non-digestible or slow rate of digestion materials, including: aplastic material, such as a resin, a resinoid, a polymer, a cellulosederivative, a casein material, and/or a protein; a metal, including acombination of metals/alloy; a glass material; a ceramic; a compositematerial; and/or other material/combination of materials. In aparticular embodiment, acoustically transmissive encapsulation 208 maybe comprised of a material that aids in the sensing of biological,chemical, or other attributes of body material that touches or comes inclose proximity to the acoustically transmissive encapsulation 208, suchas could be called an integrated encapsulation and sensor material.

After being swallowed by human 102, ingestible capsule 104 eventuallypasses from human 102, such as when human 102 has a bowel movement toexcrete waste. In an embodiment, ingestible capsule 104 is disposable.In another embodiment, ingestible capsule 104 may be recovered, (andrecycled) for reuse.

Depending upon the ability or control of the patient, ingestible capsule104 may alternatively be inserted into a lower gastrointestinal tract ofhuman 102 as a suppository device.

Depending on the configuration of sensor 202, while passing throughhuman 102, ingestible capsule 104 can sense conditions and/or featuresof any part of the gastrointestinal tract, and any of thematerials/fluids contained within and/or secreted by the organs in thegastrointestinal tract or organs indirectly associated with thegastrointestinal tract. Ingestible capsule 104 can also receiveconditions or signals from even more remote body organs such as acousticpickup of heartbeat and/or breathing and more indirect conditions suchas temperature. In an embodiment, a camera is coupled to ingestiblecapsule 104 to allow visual observation of human 102.

As mentioned, ingestible capsule 104 transmits information incommunication signal 106 to be received outside human 102, such as bycomputing device 108. In an embodiment, computing device 108 may beconfigured to communicate with a remote entity 502, such as shown in anexample sensor communications network 500 shown in FIG. 5. Computingdevice 108 may be configured to communicate with remote entity 502 usingwired and/or wireless links, in a direct fashion or through a network504. For example, computing device 108 transmits a communication signal506 to network 504, which transmits a communication signal 508 to remoteentity 502. Network 504 may be any type of network or combination ofnetworks, such as a telephone network (e.g., a land line and/or cellularnetwork), a personal area network (PAN), a local area network (LAN),and/or a wide area network (WAN) such as the Internet.

Remote entity 502 may be one or more of a variety of entities, includinga human and/or computer-based entity. For example, remote entity 502 mayinclude a doctor who receives information collected by ingestiblecapsule 104 (and optionally processed by computer device 108) incommunication signal 508.

As shown in FIG. 5, sensor communications network 500 may include areturn communications path from remote entity 502 through network 504 tocomputing device 108. For example, a return communication signal 510 istransmitted by remote entity 502 to network 504, which transmits areturn communication signal 512 to computing device 108. In this manner,remote entity 502 (e.g., doctor and/or computer system) can providefeedback to computing device 108 in communication signal 512 regardingthe analysis of human 102 performed by ingestible capsule 104. Returncommunication signal 512 may include any type of data/information formatfor providing the feedback, including an email, a text message, a textfile, a document formatted for commercially available word processingsoftware, a proprietary document/data format, auditory alarms, alertsand messages, etc.

Ingestible capsule 104 may also communicate with computing device 108via an intermediate sensor link module 602, as shown in FIG. 6. Sensorlink module 602 receives communication signal 106 from ingestiblecapsule 104. Sensor link module 602 transmits a communication signal 604to computing device 108, to provide the information sensed by sensor 202to computing device 108. For example, sensor link module 602 may be usedwhen ingestible capsule 104 communicates using an acousticcommunications signal having a power level too low to reliably bereceived by computing device 108. As shown in FIG. 6, sensor link module602 is coupled to human 102.

In another embodiment, sensor link module 602 may provide acommunication interface between ingestible capsule 104 and network 504,such that a separate computing device 108 is not required. In such anembodiment, sensor link module 602 may perform some or all functions ofcomputing device 108 described above, and thus sensor link module 602may be referred to as a computing device.

Multiple sensor link modules 602 may provide a capability of locationdetection through triangulation and other algorithms, capable ofdetecting sensor device 104 to a very accurate, three (3) dimensionallocation within human 102. In an embodiment, multiple sensor linkmodules 602 may be attached to human 102 at various locations in orderto receive the interior acoustic signal from different positions. Sensorlink module 602 may be, for example, directly attached to the skin ofhuman 102, such as by an adhesive or a strap. Sensor link module 602 maybe attached to human 102 in one or more locations, including the head,neck, chest, back, abdomen, arm, leg, etc. With regard to receivingcommunication signal 106 from ingestible capsule 104 passing through thegastrointestinal tract, ingestible capsule 104 may be attached to theneck, chest, back, and/or abdomen for a short signal path.

An amount of received information is in part proportional to the numberof sensor link modules 602 attached to human 102. The array of sensorlink modules 602 may be attached at specific locations on human 102 toincrease, and even maximize, the received diagnostic information.Multiple sensor link modules 602 can identify a specific location of theingestible capsule 104 which can be used for linking a location to thedetection of a sensed material. The location can also be used toidentify a historical analysis of the track taken by the ingestiblecapsule and the speed of passage.

For example, the attachment of an array of three or more sensor linkmodules 602 to human 102 may enable triangulation or other locationfinding algorithms to be used to locate ingestible capsule 104 in human102. Alternatively, one or more sensor link modules 602 having three ormore receivers each may be used to the same effect. Further detailsregarding location of an ingestible capsule may be found in co-pendingU.S. Patent Appl. Ser. No. 11/851,179, titled “Imaging and LocatingSystems and Methods for a Swallowable Sensor Device,” incorporated byreference herein in its entirety. By locating ingestible capsule 104 inhuman 102, a location of a sensed material in human 102 can bedetermined.

In embodiments, sensor link module 602 may be configured in variousways. For instance, FIG. 7 shows an example sensor link module 602,according to an embodiment of the present invention. As shown in FIG. 7,sensor link module 602 includes a control logic 702, a sensorcommunication module 704, a storage 706, a remote communication module708, and a power source 710.

Sensor communication module 704 receives communication signal 106 fromingestible capsule 104. Sensor communication module 704 demodulates thesensor-related information of communication signal 106. Furthermore,sensor communication module 704 may process and/or convert a format ofthe information received in communication signal 106. For example,sensor communication module 704 may perform an analog-to-digital (A/D)conversion of the received sensor information, and outputs a sensorinformation signal. The sensor information signal may be received bystorage 706 and/or by control logic 702. In an embodiment, sensor linkmodule 602 may convert a communications signal 106 (for example, anacoustic protocol) into an industry adopted or standardizedcommunications signal 604 (for example, Medical Implant CommunicationsServices (MICS), an RF medical devices standardized protocol). Such anembodiment may not require much storage 706, potentially as small as asingle register device.

In other embodiments, storage 706 is configured to store the sensorinformation of the sensor information signal. Storage 706 may includeany type of suitable storage, including a hard drive and/or memorydevices. For example, in an embodiment, storage 706 includes aread/write non-volatile memory, such as a secure digital (SD) memorycard as is typically used in a PDAs and digital cameras. Storage 706 canoutput the stored information in a stored sensor information signal, forsubsequent transmission to computing device 108 by remote communicationmodule 708. In an embodiment with a removable storage 706 (SD memory,for example), physical removal of the memory and insertion intocomputing device 108 or remote entity 404 may be both possible and costeffective.

Control logic 702 is configured to control operation of sensor linkmodule 602.

Remote communication module 708 receives the stored sensor informationsignal, and formats the sensor-related information for transmission.Furthermore, remote communication module 708 transmits the sensorinformation in communication signal 604. Remote communication module 708may be configured to transmit communication signal 604 in a variety offormats/protocols, such as a standard RF communication protocolincluding Bluetooth, IEEE 802.11, Zigbee, or other communicationprotocol, standard or otherwise. For example, in embodiments, computingdevice 108 may be a Bluetooth, 802.11, and/or Zigbee configured handhelddevice such as cell phone, personal digital assistant (PDA), aBlackberry™, wrist watch, music player, or laptop, or other type ofcomputer, handheld, desktop, or otherwise. Remote communication module708 may also transmit an identification number assigned to ingestiblecapsule 104 for identification by a receiver.

Power source 710 provides power to elements of sensor link module 602that require power, such as control logic 702, sensor communicationmodule 704, storage 706, and remote communication module 708. Forexample, power source 710 may include one or more batteries that arerechargeable or non-rechargeable. Power source 710 may also (oralternatively) include an interface for externally supplied power, suchas standard AC power.

As described above, in an embodiment, ingestible capsule 104 cantransmit an acoustic signal. By receiving the acoustic signaltransmitted by ingestible capsule 104, sensor link module 602 mayperform a type of ultrasound analysis based on the human interiorgenerated acoustic signal from ingestible capsule 104. As acousticcommunication signal 106 is transmitted through human 102 fromingestible capsule 104, signal 106 is transformed by attenuation,refraction, and reflection, as a function of the tissue of human 102that signal 106 passes through. The transformed signal thus providesadditional diagnostic information to sensor link module 602, very muchlike a diagnostic ultrasound conveys diagnostic information that can beanalyzed by a trained technician. The acoustic signal from ingestiblecapsule 104 may be viewed as an “interior” ultrasound or “sonogram”,which can be analyzed to extract additional diagnostic informationregarding human 102. In an embodiment, information received by sensorlink module 602 regarding the interior ultrasound signal can be used togenerate a graphical display of at least a portion of the interior ofhuman 102.

III. Example Computer System Embodiments

According to an example embodiment, an ingestible capsule may executecomputer-readable instructions to perform its functions. Furthermore, asensor link module for communicating with the ingestible capsule mayexecute computer-readable instructions to communicate with theingestible capsule. Still further, a computing device may executecomputer-readable instructions to communicate with the ingestiblecapsule and/or the sensor link module, and/or to process informationobtained by the ingestible capsule and/or sensor link module, asdescribed above. Still further, a test kit and medical diagnosticnetwork system may each execute computer-readable instructions toperform its functions.

In one embodiment, one or more computer systems are capable of carryingout the functionality described herein. An example of a computer system800 is shown in FIG. 8.

The computer system 800 includes one or more processors, such asprocessor 804. The processor 804 is connected to a communicationinfrastructure 806 (e.g., a communications bus, cross-over bar, ornetwork). Various software embodiments are described in terms of thisexemplary computer system. After reading this description, it willbecome apparent to a person skilled in the relevant art(s) how toimplement the invention using other computer systems and/orarchitectures.

Computer system 800 can include a display interface 802 that forwardsgraphics, text, and other information from the communicationinfrastructure 806 (or from a frame buffer not shown) for display on thedisplay unit 830.

Computer system 800 also includes a main memory 808, preferably randomaccess memory (RAM), and may also include a secondary memory 810. Thesecondary memory 810 may include, for example, a hard disk drive 812and/or a removable storage drive 814, representing a floppy disk drive,a magnetic tape drive, an optical disk drive, etc. The removable storagedrive 814 reads from and/or writes to a removable storage unit 818 in awell known manner. Removable storage unit 818 represents a floppy disk,magnetic tape, optical disk, etc. which is read by and written to byremovable storage drive 814. As will be appreciated, the removablestorage unit 818 includes a computer usable storage medium having storedtherein computer software and/or data.

In alternative embodiments, secondary memory 810 may include othersimilar devices for allowing computer programs or other instructions tobe loaded into computer system 800. Such devices may include, forexample, a removable storage unit 822 and an interface 820. Examples ofsuch may include a program cartridge and cartridge interface (such asthat found in video game devices), a removable memory chip (such as anerasable programmable read only memory (EPROM), or programmable readonly memory (PROM)) and associated socket, and other removable storageunits 822 and interfaces 820, which allow software and data to betransferred from the removable storage unit 822 to computer system 800.

Computer system 800 may also include a communications interface 824.Communications interface 824 allows software and data to be transferredbetween computer system 800 and external devices. Examples ofcommunications interface 824 may include a modem, a network interface(such as an Ethernet card), a communications port, a Personal ComputerMemory Card International Association (PCMCIA) slot and card, etc.Software and data transferred via communications interface 824 are inthe form of signals 828 which may be electronic, electromagnetic,optical or other signals capable of being received by communicationsinterface 824. These signals 828 are provided to communicationsinterface 824 via a communications path (e.g., channel) 826. Thischannel 826 carries signals 828 and may be implemented using wire orcable, fiber optics, a telephone line, a cellular link, a radiofrequency (RF) link and other communications channels.

In this document, the terms “computer program medium” and “computerusable medium” are used to generally refer to media such as removablestorage drive 814 and a hard disk installed in hard disk drive 812.These computer program products provide software to computer system 800.The invention is directed to such computer program products.

Computer programs (also referred to as computer control logic) arestored in main memory 808 and/or secondary memory 810. Computer programsmay also be received via communications interface 824. Such computerprograms, when executed, enable the computer system 800 to perform thefeatures of the present invention, as discussed herein. In particular,the computer programs, when executed, enable the processor 804 toperform the features of the present invention. Accordingly, suchcomputer programs represent controllers of the computer system 800.

In an embodiment where the invention is implemented using software, thesoftware may be stored in a computer program product and loaded intocomputer system 800 using removable storage drive 814, hard drive 812 orcommunications interface 824. The control logic (software), whenexecuted by the processor 804, causes the processor 804 to perform thefunctions of the invention as described herein.

In another embodiment, the invention is implemented primarily inhardware using, for example, hardware components such as applicationspecific integrated circuits (ASICs). Implementation of the hardwarestate machine so as to perform the functions described herein will beapparent to persons skilled in the relevant art(s).

In yet another embodiment, the invention is implemented using acombination of both hardware and software.

IV. Acoustic Information Exchange

Because signals are transmitted between ingestible capsule 104 and anexternal receiver and/or transmitter, the signals necessarily passthrough living tissue of human 102. To minimize damage to the tissue,ingestible capsule 104 is configured for low power operation, includingextreme low power (XLP) operation. Operating at a lower power thanexisting camera pills or radio frequency (RF) based pills enablesingestible capsule 104 to have a smaller, longer-lasting battery thanexisting pills. Low power operation also provides the flexibility toallocate power to functions of ingestible capsule 104 other thaninformation exchange without sacrificing size. For example, reducing thepower for information exchange enables additional power to be used todrive multiple sensors.

Ingestible capsule 104 can achieve low power communications by usingacoustic signals for information exchange. The acoustic channel candeliver reliable information (e.g., a signal having a signal-to-noiseratio of approximately 15 dB) with a total required transmission poweras low as a few microwatts, depending on the amount of information thatis transmitted. Such low power is a possibility because ingestiblecapsule 104 need not transmit the signal any farther than approximately20 cm (e.g., from the innermost point in human 102 to a detector on theskin of human 102).

As discussed with respect to FIG. 3, ingestible capsule 104 may includean acoustic communications module, such as acoustic communicationsmodule 302, configured to transmit and/or receive an acousticcommunications signal. For the acoustic transmitter to effectivelytransmit a signal for detection outside the body, the signal must have arelatively high signal-to-noise ratio (SNR), such as, for example, 15dB. Methods and systems for increasing the SNR will be described furtherbelow. Additionally, since the pill may rotate or otherwise changeorientation while inside human 102, the acoustic signal should betransmitted substantially omnidirectionally.

In an embodiment, omnidirectionality can be obtained by creation of aspherical transducer that launches a spherical wave front. In anotherembodiment, omnidirectionality may be implemented with multipletransducers having a more directional radiation pattern utilized insequential time periods transmitting the same information on multipletransducers. Orientation of these transducers is most efficient when theorientations of the peak signal are orthogonally placed within a finalconfiguration. The number of transducers, the amount of information sentin a time period, and the algorithm employed to switch to another timeperiod and transducer may be determined by a person having skill in theart without departing from the spirit and scope of the presentinvention.

As previously described, FIG. 4 shows a spherical embodiment ofingestible capsule 104, wherein signal 106 is transmittedomnidirectionally via a single acoustic transducer. When signal 106 istransmitted from the single acoustic transducer, signal 106 interactswith various surfaces, for example, the internal tissue and skin ofhuman 102. Interaction with these surfaces results in one or both ofreinforcement reflections and cancelling reflections that may interferewith signal 106. As a result, some of the information carried in signal106 may be corrupted by the time it reaches an external receiver.Further, if the receiver is located at a null in the signal, noinformation will be received at all. In an embodiment, multiple externalreceivers may be utilized. Reflections (constructive or destructive) mayinterfere with signal 106, resulting in different signals being receivedby each of the multiple external receivers. Such an embodiment allowssignal 106 to be received from one external receiver even when signal106 is too distorted to be correctly detected on an external receiver.

FIG. 9 illustrates an alternative embodiment of an ingestible capsule104 that reduces problems with interfering signals. Ingestible capsule104 is capsule-shaped, and includes two acoustic transducers, 904 a and904 b. In an embodiment, acoustic transducers 904 a and 904 b are eachplaced at an equal distance from their respective ends. Transducer 904 atransmits an output signal 106 a. Transducer 904 b transmits an outputsignal 106 b. Due to the placement of transducers 904 a and 904 b nearthe ends of ingestible capsule 902, the combined effect of outputsignals 106 a and 106 b is an output signal having a uniformity similarto that of an omnidirectional transmitter. Furthermore, if transducers904 a and 904 b are appropriately spaced, nulls in the output signal canbe eliminated. For example, if the spacing between transducers 904 a and904 b is approximately one-half the wavelength of the transmittedsignal, a signal produced by one transducer will be received even whenthe signal produced by the other transducer is at a null.

In another embodiment, transducers 904 a and 904 b need not be locatedwith specific spacing or orientation referenced to a frequency ofoperation as depicted in FIG. 9. In this embodiment, information can betransmitted during a first time period on transducer 904 a, providingsignal 106 a to be received by one or multiple external receivers.Subsequently, a duplicate set of information may be transmitted during asecond time period on transducer 904 b, providing signal 106 b to bereceived by one or multiple external receivers. By having differentorigins of signals 106, but the same content, an external receiver islikely to properly receive a signal 106 b in the event that signal 106 ahas been severely impacted by destructive interference caused byreflections of the signals off a variety of body parts and cavities.While FIG. 9 depicts use of two transducers, the use of three or moretransducers gains more probability that signals are received and do notdepart from the scope and spirit of this invention.

FIG. 10 shows an example circuit 1000 for acoustic communications module402, according to an embodiment of the present invention. As shown inFIG. 10, circuit 1000 includes an oscillator 1002, an amplifier 1004,and an acoustic transducer 1006. In the example of FIG. 10, sensor 1012has a resistance (or other impedance value) that changes based on thesensed stimulus, stimulus 1010. For example, sensor 1012 may be atemperature sensor. Sensor 1012 is coupled in series with oscillator1002, which may be a current-dependent oscillator configured to operatein a deep-threshold voltage (Vt) range to lower an oscillation frequencygenerated by oscillator 1002 to a desired acoustic frequency range. Asthe resistance of sensor 1012 changes, the oscillator frequency changesin a predictable way. An output of oscillator 1002 is coupled to aninput of an amplifier circuit 1004 for amplification. An output ofamplifier 1004 is input to acoustic transducer 1006 (which may includeor be coupled to an acoustic radiating element or acoustic actuator)that acts as a “speaker” to send the acoustic information out in anacoustic communication signal 106. Acoustic transducer 1006 may be, forexample, one or more piezoelectric transducers. Although acoustictransducer 1006 is described as being used for transmitting a signal,one of skill in the art will recognize that acoustic transducer 1006 mayalso be used to receive an incoming acoustic signal. Additionally,although circuit 1000 is discussed herein as transmitting sensorinformation, one of skill in the art will recognize that circuit 1000may also be modified to receive information from transducer 1006.Further, although circuit 1000 is discussed herein as transmittingsensor information, one of skill in the art will recognize that circuit1000 may also be used to transmit acoustic signals used for imagingand/or locationing without departing from the spirit and scope of thepresent invention.

In another embodiment, no oscillator is needed to drive oscillation ofacoustic transmitter 1006. Instead, an electromechanical modulationmethod using only a DC voltage instead of an internal oscillator may beused to modulate information into output signal 106. Theelectromechanical modulation method takes advantage of the nature ofpiezoelectric elements to expand or contract in response to an appliedvoltage. If voltage is applied in an appropriate manner, the resultingexpansion or contraction of the piezoelectric element can be indicativeof “1” and “0” bits in an information stream.

FIG. 11 is a block diagram illustrating a cross-section of an exemplarypiezoelectric transducer 1102 for modulating information into outputsignal 106 using electromechanical modulation. In FIG. 11, a voltage Vis coupled across piezoelectric transducer 1102. When voltage V is equalto 0 V, piezoelectric transducer 1102 is uncompressed and has a givenacoustic impedance. When voltage V is greater than 0, piezoelectrictransducer 1102 is compressed (e.g., clamped), which increases thespring force. This compression makes piezoelectric transducer 1102stiffer, changing the acoustic impedance of piezoelectric transducer1102. Piezoelectric transducer 1102 thus has a first resonant frequencyat 0 V and a second resonant frequency at the higher voltage.

A step function may be applied to piezoelectric transducer 1102 to takeadvantage of the resonant frequency variation. FIG. 12 illustrates anexemplary step function 1202. At point 1204, the voltage acrosspiezoelectric transducer 1102 is suddenly increased from, for example, 0V to 10 V. Although this example will be described with using a lowvoltage of 0 V and a high voltage of 10 V, one of skill in the art willrecognize that any two voltages having a differential may be usedwithout departing from the spirit and scope of the present invention. Asa result, piezoelectric transducer begins ringing at a frequencyF_(10V). At point 1206, the voltage across piezoelectric transducer 1102is suddenly decreased from, for example and without limitation, 10 V to0 V. As a result, piezoelectric transducer changes impedance and beginsringing at a frequency F_(0V) that is different from frequency F_(10V).

The sudden changes in applied voltage in step function 1202 are similarto a tuning fork being struck. As a result, piezoelectric transducer1102 rings at a self-resonance value with no additional energy applied.This makes electromechanical modulation useful for low power situations.Information bit values can be assigned to the frequencies at whichpiezoelectric transducer 1102 rings. For example, the frequency at whichpiezoelectric transducer 1102 rings when subject to a voltage at 10 Vmay indicate a “1” bit, while the frequency at which piezoelectrictransducer 1102 rings when the voltage is dropped to 0 V may indicate a“0” bit.

An intermediate voltage may be utilized in electromechanical modulationto provide a drone frequency that separates out sequential bits in aninformation stream. FIG. 13 illustrates an exemplary waveform 1300 forproviding a high frequency, a low frequency, and a drone frequency toproduce an information stream. In this example, an intermediate voltageof 5 V is used between bits to provide bit separation. Waveform 1300begins at point 1302 with the application of a 5 V signal, causingpiezoelectric transducer 1102 to ring at a drone frequency, f_(D). Atpoint 1304, a 10 V signal is applied to piezoelectric transducer 1102.As a result, piezoelectric transducer 1102 resonates at a frequencyf_(10V), which may represent, for example, a “1” bit. At point 1306,after the resonance of piezoelectric transducer 1102 has faded due todamping in piezoelectric transducer 1102, voltage V is returned to 5 V.The drop from 10 V to 5 V causes piezoelectric transducer 1102 to ringat drone frequency f_(D). At point 1308, a 10 V signal is applied,causing piezoelectric transducer 1102 to ring at frequency f_(10V)again, producing another “1” bit. At point 1310, after the resonance ofpiezoelectric transducer 1102 has faded, voltage V is returned to 5 V,causing piezoelectric transducer 1102 to ring at drone frequency f_(D).At point 1312, voltage V is dropped to 0 V. The drop causespiezoelectric transducer 1102 to resonate at a frequency f_(0v), whichmay represent, for example, a “0” bit. At point 1314, after theresonance of piezoelectric transducer 1102 has faded, voltage V isreturned to 5 V, causing piezoelectric transducer 1102 to ring at dronefrequency f_(D). In this manner, waveform 1300 provides a “1-1-0”signal.

The amount of time it takes the resonance of piezoelectric transducer1102 to dampen out after each voltage is applied depends on the Q of theresonator. The receiver can be set accordingly to receive the low powerinformation communication modulated using electromechanical modulation.Since piezoelectric transducer 1102 uses only a DC voltage in thisembodiment and does not use an oscillator to drive piezoelectrictransducer 1102, leakage in the circuit is similar to loss in acapacitor and the power level required is approximately 1/1000 the powerrequired to use electromagnetic signals (such as RF).

When a signal is transmitted from ingestible capsule 104, the vibrationof, for example, piezoelectric transducer 1102 in communications module204 may interfere with the operation of sensor 202. Control logic 604can be configured to enable or disable operation of sensor 202 and/orcommunications module 204 at various times during the transit ofingestible capsule 104 through, for example, the gastrointestinal tract.Control logic 604 may enable or disable operation of elements ofingestible capsule 104 based on time and/or location of ingestiblecapsule 104. For example, control logic 214 may include a timing module.The timing module of control logic 214 may be used to enable and disablesensor 202 and/or communication module 204 in a periodic manner or atpredetermined time intervals, so that sensor information is transmittedat set times.

In an embodiment, a sensor 202 a may interfere with signals 106, andshould therefore be sampled only when signals 106 are not present insufficient energies, such as would be adjacent to communications module204. For example, there may exist a standard standoff period after eachinformation exchange that allows new, non-corrupted information to betaken by sensor 202. During this standoff period, sensor 202 may beactivated and sensor readings read and stored. After the standoff periodends, the acoustic communications module may be re-activated fortransmission. After transmission, a new standoff period begins. Inanother embodiment, however, sensor 202 may only be valid when in thepresence of signal 106, such as with an acoustic receiver sensor tomatch in frequency with signal 106. In this embodiment, it is alsolikely that sensor 202 requires a signal of comparison electricallyconnected to communications module 204. Such a device results in sensingthe reflectivity of tissue surrounding device 104, for example, aself-contained localized ultrasonic imaging device. Additionally, such adevice is efficient in that a reference signal for imagery is derivedfrom a communications signal 106, not a separate signal requiring morepower, and hence a larger device 104.

Control logic 214 may be configured to gate power from power source 206to sensor 202 and/or communications module 204, or to gate them in othermanners to enable or inhibit their operation as desired. Alternatively,control logic 214 may receive information from sensor(s) 202 todetermine a relative location of ingestible capsule 104 ingastrointestinal tract 300. Based on the determined location, controllogic 214 may enable or disable operation of communications module 204and/or sensor 202. Furthermore, control logic 214 may also placecommunications module 204 and/or sensor 202 in a power conservationmode, for example a reduced power signal 106, when in close proximity toan external receiver and/or reduced sensor activity. Alternatively,control logic 214 may instigate a cycle based on sensor activity and/orlocation.

V. Phased Array Sensor Link Module

As described above with respect to FIG. 6, ingestible capsule 104 maycommunicate with a sensor link module acting as an intermediary to or inlieu of computing device 108. Sensor link module 602 may be coupled tohuman 102 in a variety of ways. For example, sensor link module 602 maybe directly attached to the skin of human 102, such as by an adhesive ora strap. Sensor link module 602 may be incorporated in a patch fordirect attachment to a surface, such as skin, of human 102. An adhesivelayer may be coupled to sensor link module 602. The adhesive layer mayinclude, for example, an adhesive commonly used in transdermal patches.

In one embodiment, each sensor link module 602 includes a singleacoustic transducer, and multiple patches can be used to triangulate thelocation of an ingestible capsule, receive information exchanges fromthe ingestible capsule, and/or transmit information to the ingestiblecapsule. In another embodiment, a single sensor link module 602 includesmultiple acoustic transducers. The transducers are organized into anarray, receive information exchanges from the ingestible capsule, and/ortransmit information to the ingestible capsule. Additionally,transducers organized into an array can facilitate an accurate location,whereby phase differences between the transducers are used to calculatethe direction (angle) of the ingestible capsule; in combination,amplitudes of signals between the transducers at the same or differentfrequencies derive distance. The combination creates an accuratelocation of device 104.

FIG. 14 is an illustration of an exemplary phased array 1400 for use asa sensor link module according to an embodiment of the presentinvention. Phased array 1400 includes multiple acoustic transducers1402. Although FIG. 14 illustrates an array of nine acoustic transducers1402 a-1402 i, one of skill in the art will recognize that any number ofacoustic transducers 1402 may be used without departing from the spiritand scope of the present invention. Further, one of skill in the artwill recognize that acoustic transducers 1402 may be placed in anypattern, such as a grid pattern or a close-packed hexagonal arraypattern.

An array of acoustic transducers 1402 allows triangulation to beperformed using a single sensor link module when a device, such asingestible capsule 104, emits a signal 1404. Signal 1404 may be aninformation signal, such as information signal 106, or it may be alocationing signal emitted, for example, prior to the emission ofinformation signal 106. As illustrated in FIG. 14, signal 1404 hasvarious wavefronts.

The phase of the signal detected by a given acoustic transducer 1402will vary, depending on the location of ingestible capsule 104 relativeto the given acoustic transducer 1402. The operating wavelength λ ofingestible capsule 104 determines the size and location of each acoustictransducer 1402. If each acoustic transducer has a width of λ/4 and isseparated from other acoustic transducers by a distance of λ/4, suchthat the distance between the centers of two adjacent acoustictransducers is λ/2, different phases of each signal period can bedetected by the various acoustic transducers 1402. The different phasesand amplitudes of signal 1404 as detected by multiple acoustictransducers 1402 can then be used to pinpoint the location of ingestiblecapsule 106 relative to the sensor link module by calculation of angleand distance from the phase and amplitude, respectively, of signal 106as it is received by transducers 1402.

Because the signal is acoustic, however, it can be difficult to ensurethat the signal detected by transducer 1402 is at its peak at a combinedreception point 1408 for input to receiver 1410, which is needed foraccurate locationing. To solve this difficulty, an adjustable delay 1406may be coupled to each acoustic transducer 1402. In an embodiment, eachadjustable delay 1406 automatically adjusts itself to achieve maximumgain at a peak signal amplitude with respect to a combined signal atpoint 1408, or alternatively with respect to a single reference signalsuch as element 1402 a, similarly to a radio frequency phased arrayconstruction. In another embodiment, a separate circuit may adjustdelays 1402 a-1402 i. Detection of the peak signal amplitude at amaximum gain (thus maximizing SNR) may occur based on, for example,successive approximation or a previous location measurement. Use of asuccessive approximation method is possible because received acousticsignal 1404 is moving much more slowly than the time it takes todigitally process received signal 1404. For example, using a 1 MHzdigital signal processor, all the calculations needed to focus on thesignal can be performed more quickly than the signal changes.

For example, in FIG. 14, a first portion of a wavefront (e.g., a portionof signal 1404 assigned a 0° phase delay) of signal 1404 is detected byacoustic transducers 1402 a, 1402 e, and 1402 i. A second portion ofwavefront of signal 1404 detected by acoustic transducers 1402 d and1402 h differs from the first portion of wavefront of signal 1404 by90°. A third portion of wavefront of signal 1404 detected by acoustictransducer 1402 g differs from the first portion of wavefront of signal1404 by 180°. Therefore, the maximum gain of the signal is produced whena value of 0° is assigned to phase delay 1406 g, a value of 900 isassigned to each of phase delays 1406 d and 1406 h, and a value of 180°is assigned to each of phase delays 1406 a, 1406 e, and 1406 i. Toachieve the maximum gain of the system, all wavefront peaks should bealigned at the output of adjustable delays 1406 a-1406 i.

Once the phase footprint of signal 1404 is determined, the phasefootprint can be used to identify the location of ingestible capsule104. That is, the phase separation of the different acoustic transducers1402 identify the angular direction of ingestible capsule 104 while thedifferences in time of arrival between acoustic transducers 1402indicate a distance to ingestible capsule 104.

The same phase information can also be used to maximize the SNR of aninformation signal received from ingestible capsule 104, such as outputinformation signal 106. In an embodiment, a primary wavefront fromdevice 104 is phase aligned throughout all transducers 1402 a-1402 i.However, acoustic noise is typically produced by reflections fromobjects within the human 102 and also the exterior skin of human 102.Reflections likely do not originate from the same angle with respect tothe array 1402. Thus, the combined noise signal output at point 1408 isreduced from maximum signal as the reflections, originating from anoff-angle position, are partially phase cancelled due to the delays setupon 1406 a-1406 i. Output information signal 106 can thus betransmitted at a lower power than is required for systems that do nothave as high a SNR. That is, systems that are not optimized to receive atransmitted signal at maximum gain require a higher-power transmission,in case the signal is received off-peak and/or the noise is notpartially phase cancelled, making the SNR relatively low. In the presentembodiment, however, the signal is received on-peak and most reflectedsignals are partially phase cancelled so the SNR is relatively high. Thepower of the signal thus need not be as strong. This technique istherefore useful in an environment where low-power signals arepreferable, such as the human body where signals are passing throughlive tissue.

Another advantage of the phased array design is that the potentialangles of reception are extremely wide for an instance of thetechnology, whereas a larger receiver to provide signal gain istypically very narrow. For example, an example element nine times thesize of transducer 1402 would provide potentially the same gain as theFIG. 14 array; however, this occurs only when device 104 isperpendicular to a flat receiving side of a large element. Furthermore,at an angle of 45 degrees, for example, the combined signal received byan maximized array far exceeds the output of the same single elementnine times larger. This is due to the wavefront cancellation within alarge element on an off-perpendicular wavefront, such as is the case foran acoustic signal transmitted and received within a human body 102.

Further, once the location of ingestible capsule 104 is determined,phased array 1400 can also be used to focus an information exchangesignal on ingestible capsule 104 in order to send information fromphased array 1400 to ingestible capsule 104. To do this, a known phasedelay 1406 a-1406 i, such as a captured configuration from a signalreception, is implemented into a signal transmitted from an amplifier1412, with the resulting phase delayed signal routed to transducers 1402a-1402 i respectively. Because the transmission is focused on ingestiblecapsule 104, such that the point of maximum gain intersects with thelocation of ingestible capsule 104, either a lower average power signalmay be used. Alternatively, a less sensitive (lower power) receiverdesign within sensor device 104 may be used.

Although locationing and information exchange are described in FIG. 14with respect to a phased array in a single sensor link module, one ofskill in the art will recognize that improved resolution may be providedwhen additional sensor link modules, each having its own phased array,are used. Furthermore, one of skill in the art will also recognize thatmultiple phased array devices can utilize phase-only information for theaccurate determination of the location of sensor device 104, as multipleintersecting lines derived from multiple angles intersect at a point oforigin of the signal from device 104.

In an alternate embodiment, multiple single element receivers and/orsensor link modules 602 exist and forward signals received to computingdevice 108. As described earlier, a desired signal 104 may be incidentupon each of sensor link modules 602 in combination with reflectionsfrom a variety of body parts within and on (e.g., located on the skinof) human 102. Therefore, a computing device 108 can create a complexmathematical model (e.g., a Fourier transform) of the complex signalreceived. Given a particular received frequency of operation F1 ofsensor device 104, computing device 108 may derive a close proximity toactual signals received by a combination of F1 at an amplitude A1, andphase P1; a second harmonic at frequency F2 (necessarily at F1×2), itsamplitude A2, and phase P2, and so on for 3^(rd) harmonic, 4^(th)harmonic, and further frequencies as is well known as a Fouriertransform. The closeness to actual signals is primarily a function ofhow many harmonics can be evaluated, and the resolution of amplitude andphase. Furthermore, computing device 108 performs this Fourier transformon each of the associated sensor link modules 602. The resultinganalysis can be utilized to algorithmically combine signals from sensorlink modules 602 for a maximum signal reception. Additionally, it can beutilized to minimize an out of phase reflection (considered in this caseas noise).

In a further implementation of this embodiment, the resulting analysisof a received signal 104 at sensor link modules 602 can be utilized in areverse manner, regenerating known frequencies, phases, and amplitudesof harmonics F1, F2, F3, and so on. This Inverse Fourier transformprovides an environment of three (or more) transmitted waveforms frommultiple sensor link modules 602 that maximally constructivelyinterfere, with all reflection points in the body considered, at thepoint of the original signal received from device 104. Additionally,this process must be repeated for each location of device 104, locationof sensor link modules 602 collectively, and for each transmittingfrequency utilized. A person skilled in the art will recognize that theexemplified embodiment above utilizing three sensor link modules 602 mayalso utilize any number of sensor link modules 602 to afford a desiredlevel of accuracy, including one sensor link module 602.

VI. Acoustic Biobus

The ability to modulate information into an acoustic transmission,coupled with the ability to focus the reception and/or transmission ofthe signal on a particular location to achieve maximum gain makes itpossible to use acoustic waves for many applications in addition tocommunication with an ingestible sensor device or multiple sensordevices.

One such application is communication with and control of implanteddevices, such as prosthetic controls. Currently, prosthetics require asignificant amount of wires and data paths (collectively referred toherein as a wiring harness) to effect movement of the prosthetic.According to an embodiment of the present invention, an internalacoustic biobus replaces or supplements the wiring harness of theprosthetic. FIG. 15 illustrates an exemplary biobus system according toan embodiment of the present invention. A human 1502 has a prostheticlimb 1504. An implanted prosthetic control unit 1506 receives signalsfrom brain 1508 via connection 1510. Prosthetic control unit 1506interprets the signals received from brain 1508 and modulates them intoan instruction signal. The instruction signal is transmitted byprosthetic control unit 1506 as an acoustic information signal 1512.Acoustic information signal 1512 is received by a prosthetic operationunit 1514, which causes prosthetic limb 1504 to function accordingly. Anacoustic biobus in accordance with this embodiment reduces or eliminatesthe wiring harness used for prosthetic limb 1504. Additionally,information is transmitted in a format friendly to human tissue, namely,acoustic format. Use of an acoustic biobus also reduces or eliminatesthe susceptibility of prosthetic limb 1504 to interference fromenvironmental noise, such as cellular telephone transmissions and manyother forms of radio frequency communications common in today's society.

Similarly, acoustic information signals may be communicated betweenimplantable devices, such as pacemakers, and external status and controldevices.

VII. Modulation and/or Demodulation Methods

Communications module 204 (FIG. 2) may be configured to modulateinformation from sensor output signal 212 with a carrier frequency togenerate acoustic output signal 106 according to a variety of modulationtechniques. Such techniques include, for example and without limitation,amplitude modulation (AM), frequency modulation (FM), phase modulation(PM), pulse-width modulation (PWM), and pulse-position modulation (PPM),and any combination of these modulation techniques, includingin-quadrature or other modulation schemes. Previous schemes have beenused for short commands, such as that described in U.S. Pat. No.7,024,248 to Penner et al., incorporated herein by reference in itsentirety. Such previous schemes used for short commands do not considerdifficulties present in long term and/or long stream data transmission,or communication with an ingestible capsule. For example, such previousschemes do not account for the multiple acoustic reflections and noisethat may interfere with longer periods of transmissions.

Modulation schemes are also discussed in co-pending U.S. Patent Appl.Ser. No. 11/851,236, titled “System and Method for Acoustic DataTransmission,” and co-pending U.S. Pat. Appl. Ser. No. 11/896,946,titled “Methods and Systems for Acoustic Data Transmission,” each ofwhich is incorporated herein by reference, both generally and as theypertain to acoustic data modulation/demodulation schemes.

Before further discussion of specific acoustic data transmissionmethods, it is important to describe the general acoustic environment ofthe medium, in this case human 102 (and similar for most animals ofapproximate size). Specifically, it is important to note i) how totransduce a signal, ii) what noise is to be considered, both externaland internal, and iii) what methods to use to best decode the signal inthe presence of the second item, noise.

When designing a transducer, well known principles apply to matchingwith transmitted medium. For example, a radio frequency antenna willlaunch electromagnetic waves into its environment, which includes air,buildings, etc. It is designed to assume contact with a certain medium(generally air). Similarly, a design of a speaker (and enclosure) isdesigned to be most efficient when operational at a certain normal airpressure (such as sea level). An exemplary transducer that may be usedin embodiments of the present invention assumes a characteristicenvironment of a human body 102.

Such a transducer needs to be appropriate for use within a human body,for example in contact with human tissue. Greatly different from aspeaker design in contact with air, a fluid possesses a different set ofcharacteristics. For instance, a speed of an acoustic wave in air at sealevel is approx 350 meters per second. However, a speed of an acousticwave in an animal tissue is approx 1500 meters per second. Additionally,a force required to move a volume of air is substantially different froma force required to move a volume of tissue. Thus, when designing atransducer for a human tissue, a most efficient design comes as close aspossible to matching the impedance of the medium (for example, closelymatching a speed of an acoustic wave).

Additionally, it is useful for a transducer design to focus energy inthe direction of a receiver for maximal use of energy. However, thetransducer design needs also to be able to be efficient in energytransfer for most, if not all, potential locations of a receiver whenthe transducer is mobile. In the case of an ingestible sensor device,such as ingestible sensor device 104, in a human body, the receiver isvery mobile as it transcends the full gastrointestinal tract.

Once a signal can be efficiently transmitted into a medium, the noise inthe environment should be accounted for, both from an aspect of externalnoise, but also an aspect of self-generated noise due to reflectionsfrom a variety of materials. When working with radio frequencies (RF),as commonly as they are used a key study is in the external impact ofunwanted signals from other unknown transmitters, characterized asnoise. Conversely, when evaluating an acoustic environment within ahuman body, very little, if any, noise is present from othertransmitters, given an ultrasonic frequency range. One of very fewapplications of ultrasonic signals upon a human body is in the case ofultrasound—an imaging technique by use of ultrasonic signals. However,this is not present for a general population, and a patient is typicallyunder a doctor's care when ultrasonic frequencies are being transmittedinto the body. Additionally, ultrasonic frequencies used exterior to thehuman body would need to convey internal to the body in order tointerfere with an internal transducer. Although this is possible, it isunlikely as a result of the large difference in impedance of air andhuman tissue. Ultrasonic frequencies, as a result, mostly bounce off thehuman skin to return to the air medium from which they originated.

Additionally, some common uses of RF transcend long distances almostentirely in air, such as with cellular telephony. In these cases,reflections are reasonably spaced with respect to time, and are alsovery modestly attenuated with respect to power at a receiver. Anultrasonic environment within a relatively confined space, such as ahuman body, presents a difficult noise model. Since there are bones, airpockets, differing tissues, sacks of liquids, dynamic resonating cavityeffects due to breathing, heart beat, larynx, moving fluid such as bloodflow in blood vessels, etc., causing Doppler shifting, all within closeproximity (tens and hundreds of wavelengths as opposed to tens andhundreds of thousands of wavelengths) to a transmitter and receiver,very complex waveforms are received at the receiver. These waveforms maybe a combination of a multitude of re-transmitted waveforms in the formof reflections from the original transmitted waveform imposed upon theoriginal waveform. Further complicating the acoustic model is the humanskin. The skin is an effective reflector. As effective as the skin is inreflecting airborne ultrasonic transmissions, it also reflects asubstantial amount of incident energy from within. Reflections mayinclude a reflected original wavefront, but also a reflected complexwavefront built with all of the other reflected wavefronts from thevariety of organs and materials within the body.

Timing of these reflections leads to an evaluation in three scenarios. Afirst timing scenario occurs when an original waveform is received priorto any substantial reflected waveforms from the original, referred toherein as ‘clear channel’. A second timing scenario occurs duringreception of some but not all of the complex wavefronts caused by somebut not all of the reflections, referred to herein as ‘transitionarychannel’. A third timing scenario occurs after all reflections havesubstantially stabilized, herein referred to as ‘standing wave channel’.It is noted that the standing wave channel is an adiabaticapproximation, valid for acoustic event time periods much shorter thanthe dynamic changes in the resonating cavity, due to body functions suchas heart beating and breathing. It is most important to note that amodulation of a carrier frequency (a traditional method of encoding dataupon a frequency) in any of amplitude, frequency, or phase, imposes asame environment study as does turning a carrier on and off (the extremeof amplitude modulation). The acoustic environment may therefore beanalyzed to determine clear channel, transitionary channel, and standingwave channel characteristics from the time period of the implementationof the modulation.

Differing technologies may apply to the three differing timing scenariosdescribed above, or potentially a combination of multiple technologiesto make use of multiple timing scenarios. For example, an embodiment ofthe present invention utilizes frequency hopping in order to maintainoperation within a first timing scenario, clear channel. For continuousoperation, frequencies are changed prior to the transitionary channel.As long as the frequency being hopped to was not previously sent or iscompletely attenuated from a previous transmission, it will be presentedwith a clear channel. In another example embodiment, a system makes useof a standing wave channel. Additional details of modulation schemesaccording to these and other embodiments of the present inventionfollow.

A. Drone Frequency

For example, in an embodiment, FM may be used to send the outputinformation signal 106 from ingestible capsule 104, in a variety ofschemes. For instance, an example FM protocol that can handle multiplesensors 202 a-202 c is described below:

F_(Drone) = a drone frequency, F₀ = a frequency for bit zero, F₁ = afrequency for bit 1, F_(i) = an information frequency, where i = a, b,c, etc for sensors 202a-202c, respectively, and F_(ID) = a frequencysequence of zero bits (F₀) and one bits (F₁) for an identificationnumber of the particular ingestible sensor device 104.

The drone frequency F_(Drone) is used to provide a detectable separationbetween frequencies Fa, Fb, and Fc related to information from sensors202 a-202 c. The presence of drone frequency F_(Drone) may not berequired in all implementations. Frequencies Fa, Fb, and Fc may havefrequency ranges that are non-overlapping so that communications relatedto sensors 202 a-202 c can be distinguished from each other. In anembodiment, after an ingestible capsule 104 is swallowed, the swallowedingestible capsule 104 is configured to serially send out the followingfrequency sequence:F _(Drone) F _(ID) F _(Drone) F _(a) F _(Drone) F _(b) F _(Drone) F _(c)F _(Drone) F _(ID) F _(Drone)

Thus, in a first time slot (F_(Drone)), ingestible capsule 104 transmitsthe drone frequency F_(Drone). In a second time slot (F_(ID)),ingestible capsule 104 transmits the identification number for theparticular ingestible capsule 104 as a series of 0 and 1 bits,respectively represented by frequencies F₀ and F₁. The identificationnumber may be useful, for example, when more than one ingestible capsule104 is transmitting from inside human 102.

In a third time slot (F_(Drone)), ingestible capsule 104 transmits thedrone frequency F_(Drone). In a fourth time slot (F_(a)), ingestiblecapsule 104 transmits information related to sensor 202 a. Theinformation is transmitted at a central frequency of F_(a) that variesin frequency in a manner according to information from sensor outputsignal 212 a. Thus, information from sensor 202 a is transmitted in thefourth time slot. In a fifth time slot (F_(Drone)), ingestible capsule104 transmits the drone frequency F_(Drone). In a sixth time slot(F_(b)), ingestible capsule 104 transmits information related to sensor202 b. The information is transmitted at a central frequency of F_(b)that varies in frequency in a manner according to information fromsensor output signal 212 b. Thus, information from sensor 202 b istransmitted in the sixth time slot. In a seventh time slot (F_(Drone)),ingestible capsule 104 transmits the drone frequency F_(Drone). In aneighth time slot (F_(c)), ingestible capsule 104 transmits informationrelated to sensor 202 c. The information is transmitted at a centralfrequency of F_(c) that varies in frequency in a manner according toinformation from sensor output signal 212 c. Thus, information fromsensor 202 c is transmitted in the eighth time slot. In a ninth timeslot (F_(Drone)), ingestible capsule 104 transmits the drone frequencyF_(Drone). In a tenth time slot (F_(ID)), ingestible capsule 104transmits the identification number for the particular ingestiblecapsule 104. In an eleventh time slot (F_(Drone)), ingestible capsule104 transmits the drone frequency F_(Drone). In subsequent time slots,information related to sensors 202 a-202 c can be further transmitted atfrequencies F_(a)-F_(c), and the identification number F_(ID), can befurther transmitted, separated by the drone frequency F_(D) as desired.

This frequency sequence may be received, and due to the ordering offrequency signals, and the different frequencies used, the receivedinformation from sensors 202 a-202 c can be demodulated and stored in anorganized manner.

In such embodiments, information from any number of sensors 202 can beaccommodated. In some embodiments, the drone frequency F_(D) may not benecessary. Furthermore, in some embodiments, the identification numbersequence, F_(ID), may not be necessary (e.g., if identical ingestiblecapsules 104 are individually used by human 102). Any length ofidentification number may be used.

A time interval, T_(d), may be used for each of the time slots describedabove. The time interval T_(d) may be bounded by a minimum time intervalfor T_(d), T_(dmin), and a maximum time interval for T_(d), T_(dmax). Asdiscussed above, the minimum time interval, T_(dmin), is determined bynoise issues. Here, either the standing wave model or the clear channelmodel is employed. If the standing wave approach is applied, then thesystem needs to wait for the signal to stabilize to a standing wave. Ifthe clear channel approach is chosen, then the system needs to wait forthe signal to decay before sending out a new signal on the samefrequency. The maximum time interval, T_(dmax), may be determined bypower consumption issues (such as a charge lifespan of battery 702) ofingestible capsule 104. Furthermore, a duty cycle, T_(c), may be usedfor the time slots described above. The duty cycle, T_(c), may bebounded by a minimum duty cycle length, T_(cmin), and a maximum dutycycle length, T_(cmax). The minimum duty cycle, T_(cmin), may bedetermined by requirements of the particular diagnostic test(s) to beperformed by ingestible capsule 104, and the maximum duty cycle,T_(cmax), may be determined by power consumption issues (such as acharge lifespan of battery 702) of ingestible capsule 104.

B. Spread Spectrum

i. Overview

An embodiment of the present invention is directed to acousticallytransmitting data (such as communication signal 106) from a transmitter(such as ingestible capsule 104) to a receiver (such as sensor linkmodule 602). In this embodiment, a high data rate is achieved byspreading acoustic data signals within a bandwidth considerablyexceeding the data bandwidth. The spreading scheme is based onquasi-orthogonal spreading codes having substantially zeroauto-correlation functions. Advantageously, the spreading scheme iscombined with efficient modulation schemes, thereby considerablymitigating inter-symbol interference and providing reliable systemperformance. In addition, the spreading code and modulation schemes canbe easily implemented using hardware components to reduce powerconsumption within and the size of ingestible capsule 104.

An acoustic transmission system according to an embodiment of thepresent invention includes a transmitter and a receiver. A data sourceprovides a sequence of data symbols, which may be binary or M-arysymbols. An acoustic transmitter transforms the sequence of data symbolsinto an acoustic signal by an encoding procedure and acoustic carriermodulation. Sometimes the acoustic transmitter adds a preamble packet(preamble) for synchronization and channel parameters estimation at thereceiving site.

Acoustic waves, radiated by the transmitter, propagate through anacoustic channel. The acoustic waves reach the receiver by severalpaths, reflecting from different objects, surface areas, surfaceboundaries and interfaces in the environment. This multi-pathpropagation provides a complex interference of acoustic rays, havingdifferent attenuation, phase and delay. Each acoustic ray has instable(variable) amplitude and phase (fading) because it includes severalsub-rays with insignificant delay variations.

An acoustic receiver receives random noise and the acoustic signalstransmitted by the transmitter. The acoustic receiver transforms theadditive mixture of noise and delayed signals into data symbols using ademodulation and decoding procedure as described herein.

ii. An Example System

FIG. 17 depicts a block diagram illustrating an example acoustic datatransmission system according to an embodiment of the present invention.The acoustic data transmission system of FIG. 17 includes a transmissionpath 1701 and a receive path 1751. In an embodiment, transmission path1701 is included in ingestible capsule 104 and receive path 1751 isincluded in sensor link module 602.

Transmission path 1701 includes an encoder 1710, a modulator 1712, aspreader 1714, and an acoustic transducer (transmitter) 1716.Transmission path 1701 serves to encode and modulate data to generate anacoustic signal that is transmitted through the body of human 102. Eachelement of transmission path 1701 is described in more detail below.

Encoder 1710 encodes data symbols from a data source (such as sensoroutput signal 212). The encoding scheme may include discretetransformations of data symbols, including adding redundant symbols forforward error correction (FEC).

Modulator 1712 modulates the encoded discrete signal with a carrier. Inan embodiment, modulator 1712 uses a narrow band modulation scheme, suchas phase shift keying (PSK), frequency shift keying (FSK), quadratureamplitude modulation (QAM), or the like, as described in more detailbelow. Modulator 1712 includes a carrier generator (not shown).

Spreader 1714 spreads the modulated signal according to a spreadingcode, causing the modulated signal to be spread within a bandwidth thatconsiderably exceeds the data bandwidth. In an embodiment, a spectrum ofthe modulated signal is increased by a factor of N, wherein N is thespreading factor of spreader 1714. Characteristics of the spreading codeimplemented by spreader 1714 are described below.

An ideal orthogonal spreading code sequence would completely eliminateany interference between a signal S_(r)(t) and a time delayed version ofthat signal S_(r)(t+τ). Mathematically, the amplitude A of theinterference between an ideal orthogonal spreading code satisfies thefollowing equation:

$\begin{matrix}{{A = {{\frac{1}{T}{\int_{0}^{T}{{S_{r}(t)}{S_{r}\left( {t + \tau} \right)}{\mathbb{d}t}}}} = 0}},{{{for}\mspace{14mu}{any}\mspace{14mu}{\tau }} > {T/N}}} & \left( {{Eq}.\mspace{14mu} 1} \right)\end{matrix}$where [0,T] is the data symbol interval, T is the data symbol duration,and N is the spreading factor.

Rather than implementing the ideal orthogonal spreading code of equation(1), spreader 1714 implements a quasi-orthogonal spreading code. Thequasi-orthogonal code implemented by spreader 1714 reduces interferencebetween a signal B_(r)(t) and a time-delayed signal B_(r)(t+τ) by afactor of N, wherein N is the spreading factor. In an embodiment,spreader 1714 implements a quasi-orthogonal Barker code B(t), satisfyingthe following equation:

$\begin{matrix}{{A = {{\frac{1}{T}{{\int_{0}^{T}{{B(t)}{B\left( {t + \tau} \right)}{\mathbb{d}t}}}}} = N}},{{{for}\mspace{14mu}{any}\mspace{14mu}\tau} = 0}} & \left( {{{Eq}.\mspace{14mu} 2}a} \right) \\{{A = {{\frac{1}{T}{{\int_{0}^{T}{{B(t)}{B\left( {t + \tau} \right)}{\mathbb{d}t}}}}} \leq 1}},{{{for}\mspace{14mu}{any}\mspace{14mu}\tau} > {T/N}}} & \left( {{{Eq}.\mspace{14mu} 2}b} \right)\end{matrix}$In this case spreading factor N is a number of binary elements ±1 withinthe Barker sequence (within the data symbol interval T). Equation (2)shows that side lobes of the Barker autocorrelation function do notexceed the N-th fraction of the main lobe. Thus, all widespread acousticrays (i.e., rays which are time-delayed by more than a factor of T/Nrelative to the Barker sequence in the receiver) are suppressed by Ntimes.

Spreader 1714 implements the spreading code by one or more linearoperations. These linear (parametric) operations may simply comprisemultiplication of the modulated signal and a spreading code sequence asdescribed below, although other methods for spreading the modulatedsignal may be realized without deviating from the spirit and scope ofthe present invention. In an embodiment, spreader 1714 implements an 11element Barker sequence, as described in more detail below. Other Barkersequences may be used. There are Barker sequences for N=2, 3, 4, 5, 7,11, 13. For N>13 there are not quasi-orthogonal binary sequences withA≦1. Nevertheless there are sequences with length up to N=28 for A≦2,and sequences with length up to N=34 for A≦3. For larger N, linearrecurrent M-sequences (pseudo-random binary sequences) may be used forsignal spectrum spreading; they provide about √N times suppression ofthe delayed rays.

Returning to FIG. 17, the signal from the output of spreader 1714,having N times more bandwidth than the data symbol spectrum, is fed toacoustic transducer/Tx 1716 (such as acoustic transducer 904 describedabove). Acoustic transducer/Tx 1716 converts the electrical signals fromtransmission path 1701 into acoustic signals which are then transmittedthrough the multi-path acoustic channel in the body of human 102.

After traveling through the multi-path acoustic channel, the acousticsignal is received by receive path 1751 illustrated in FIG. 17. Receivepath 1751 includes an acoustic transducer (receiver) 1760, a de-spreader1762, a demodulator 1764, and a decoder 1766. At the receiving site, thesignal from the output of acoustic transducer/Rx 1760 is subjected tothe opposite sequence of transformations compared to transmission path1701. Although the sequence of transformations is reversed, theimplementation of each method may differ substantially as ingestiblecapsule 104 is designed to be small and low power, while the sameconstraints do not necessarily apply to sensor link module 602. Avariety of implementations for transmit and receive paths areanticipated and do not depart from the spirit and scope of thisinvention. De-spreader 1762 transforms the received wideband signal intothe initial narrowband modulated signal by synchronized multiplicationof the wideband signal with the spreading code. Demodulator 1764demodulates the narrowband signal using signal processing based oncoherent or non-coherent detection schemes. Decoder 1766 distinguishesdata symbols from the demodulated signals, based on soft or harddecision decoding procedures. It should be noted that both de-spreader1762 and demodulator 1764 are controlled by a synchronization function(not shown in the FIG. 17).

It is to be appreciated that transmission path 1701 and receive path1751 are presented for illustrative purposes only, and not limitation.Variations of transmission path 1701 and/or receive path 1751 can beimplemented without deviating from the spirit and scope of the presentinvention. For example, modulator 1712 can be implemented after spreader1714. As another example, some filtration elements—such as a band-passfilter (BPF) or low-pass filter (LPF)—may be used in both transmissionpath 1701 and receive path 1751. In such examples, a narrowband BPF isused after de-spreader 1762. Such filtration elements are not depictedin FIG. 17, although their inclusion is within the spirit and scope ofthe present invention, as would be apparent to a person skilled in therelevant art(s).

iii. Example Encoding Schemes

(a) Phase Shift Keying

FIGS. 18 and 19 depict block diagrams respectively illustrating atransmission path and a receive path of an acoustic data transmissionsystem based on PSK modulation in combination with a spreading codeaccording to an embodiment of the present invention. The transmissionpath of FIG. 18 may be implemented in ingestible capsule 104 and thereceive path of FIG. 19 may be implemented in an external receiverpatch, such as sensor link module 602.

Referring to FIG. 18, the transmission path includes a PSK encoder 1810,a PSK modulator 1812, a carrier generator 1813, a spreading codegenerator (SCG) 1814, a multiplier 1815, and an acoustic transducer/Tx1816. PSK encoder 1810 together with PSK modulator 1812 and carriergenerator 1813 provide the phase modulated signals. The particularfunctions of PSK encoder 1810 and PSK modulator 1812 depend on the typeof PSK modulation scheme—whether binary PSK, binary differential PSK,M-ary PSK or M-ary DPSK, or the like. For example, if the modulationscheme is implemented as binary PSK, then PSK encoder 1810 and PSKmodulator 1812 may be implemented as a simple logic multiplier. If thePSK modulation scheme is implemented as DBPSK, then PSK encoder 1810includes a binary multiplier and a binary delay element (see, e.g.,FIGS. 20 and 22 below), and PSK modulator 1812 includes a simplemultiplier. In the case of M-ary PSK or M-ary DPSK, for instance, QPSKor DQPSK, PSK encoder 1810 may be implemented as a Gray-code encoder,and PSK modulator 1812 may be implemented as an I/Q modulator accordingto known schemes.

The phase modulated carrier from the output of PSK modulator 1812 is fedto multiplier 1815, where it is multiplied by the spreading sequence,generated by SCG 1814. SCG 1814 generates the spreading sequencesynchronously with the modulated symbols at the output of PSK modulator1812.

The wideband signal at the output of multiplier 1815 is fed to acoustictransducer/Tx 1816. Acoustic transducer/Tx 1816 transmits the acousticsignal into the multi-path acoustic channel as described above.

After traveling through the multi-path acoustic channel, the acousticsignal is received by the receive path of FIG. 19. The receive pathincludes an acoustic transducer/Rx 1960, a multiplier 1941, a SCG 1942,a synchronization unit (synch) 1943, and a PSK demodulator 1964.Acoustic transducer/Rx 1960 receives the acoustic signal and converts itinto an electrical signal. SCG 1942 and PSK demodulator 1964 arecontrolled by synch 1943, which uses both the received signal from theoutput of acoustic transducer/Rx 1960 and output signals from PSKdemodulator 1964. The particular functions and schemes of PSKdemodulator 1964 depend on both the PSK type and signal processingalgorithm. For example, if it is PSK, the conventional coherent schemebased on the carrier recovery technique is used. If it is DPSK, theconventional I/Q non-coherent scheme or even the simplestautocorrelation scheme may be used.

(b) Differential Phase Shift Keying

FIGS. 20 and 21 depict block diagrams respectively illustrating atransmission path and a receive path of an acoustic data transmissionsystem based on DBPSK in combination with a Barker spreading codeaccording to an embodiment of the present invention. The transmissionpath of FIG. 20 may be implemented in ingestible capsule 104 and thereceive path of FIG. 21 may be implemented in an external receiverpatch, such as sensor link module 602.

The transmission path of FIG. 20 includes a multiplier 2002, a delayelement 2004, a multiplier 2006, a Barker code generator 2008, amultiplier 2022, a carrier generator 2013, and an acoustic transducer/Tx2016. Referring to FIG. 20, the DBPSK encoder includes multiplier 2002and a (one bit) delay element 2004. In this scheme, a current data bitb_(k) in form of ±1 is multiplied by a result of a previousmultiplication e_(k−1) after it goes through delay element 2004. Thus,the encoded bit e_(k) that is submitted to multiplier 2006 can bewritten ase _(k) =e _(k−1) *b _(k)  (Eq. 3)

Barker code generator 2008 generates a Barker sequence. The encoded bite_(k) at the output of multiplier 2002 is subdivided into N equal partsby multiplication with the Barker sequence, containing N positive andnegative ones, in multiplier 2006. Carrier generator 2013 generates acarrier. The spreaded signal from the output of multiplier 2006,containing N positive and negative ones, modulates the carrier inmultiplier 2022. The modulated carrier is fed to acoustic transducer/Tx2016 and transmitted into the multi-path acoustic channel.

After traveling through the multi-path acoustic channel, the acousticsignal is received by the receive path of FIG. 21. The receive pathincludes an acoustic transducer/Rx 2160, a multiplier 2141, a Barkercode generator 2142, a synch 2143, and a demodulator 2164. Acoustictransducer/Rx 2160 receives the acoustic signal and converts it into anelectrical signal. Barker code generator 2142 and demodulator 2164 arecontrolled by synch 2143, which uses both the received signal from theoutput of acoustic transducer/Rx 2160 and the output signals fromdemodulator 2164. As illustrated in FIG. 21, demodulator 2164 isimplemented as an I/Q DBPSK non-coherent demodulator, which provides asubstantially perfect bit error rate (BER). In this embodiment, the BERis very close to the minimum possible BER (for example, BER=10⁻³ atSNR≈8.0 dB), at the comparatively simple implementation, which does notinclude any carrier recovery procedure.

(c) First Order And Second Order Differential Phase Shift Keying

An embodiment of the present invention uses both first order and secondorder differential phase shift keying (DPSK). Such an embodiment may beimplemented in combination with a spreading code, such as a Barkerspreading code described herein. Using first and second order DPSKprovides several advantages over conventional DPSK as described in moredetail below.

(1) Carrier Frequency Instability Problem

Digital phase-modulated signals—such as BPSK and quadraturephase-shift-keying (QPSK)—potentially provide the highest possibleperformance (i.e., the lowest BER) in noisy channels, as well as infading noisy channels. However, there are some well known difficultiesfor PSK technique application in channels with carrier frequencyinstability. If the carrier frequency changes slowly, the problem isconventionally solved by one or more of the following methods: (i)adaptive adjustment of the reference signal (carrier recoverytechniques) at the receiver; (ii) periodical transmission of thereference signal (package preamble); and/or (iii) constant transmissionof the reference signal in parallel with the data signal. Method (iii)is used in most advanced mobile wireless standards, such as WiFi, WiMax,LTE, and the like. Although these methods provide some advantages, theyall decrease the data transmission performance and complicate theoverall data transmission system.

Embodiments of the present invention that use PSK modulation in acousticdata transmission are also complicated by carrier frequency instability.In such embodiments, there are two main sources of the carrier frequencyinstability.

The first one is instability of carrier generation. For proper datatransmission, the carrier frequency instability should be less than 10⁻⁴in order to achieve a nominal bit error rate, for example. If thenominal carrier frequency F is equal to approximately 1 MHz and symbolduration T is equal to approximately 200 μs (10 kbit/s at QPSK), thenthe phase shift Δω will be given byΔω=2πΔFT=2π*100*200*10⁻⁶≈7.2°.

This phase shift does not destroy the system, but considerably decreasesits performance. For example, in a conventional PSK system aninstability of carrier generation equal to 10⁻³ completely degrades datatransmission.

The second source of the carrier frequency instability in acousticsystems is the Doppler Effect. For example, if ingestible capsule 104moves with speed 10 cm/s, then the frequency shift ΔF isΔF≈(0.1/1500)*10⁶≈67 Hz,and the phase shift Δω isΔω=2πΔFT=2π*67*200*10⁻⁶=4.8°.

So, the total phase shift, caused by both the Doppler Effect and carriergeneration instability, is about 12 degrees—i.e., about 27% of minimumdistance between signal vectors at QPSK—and therefore carrier frequencyinstability is an important problem to overcome in PSK-based acousticdata transmission systems of embodiments of the present invention.

The above-mentioned methods for addressing the carrier frequencyinstability problem consume a significant amount of power, and aretherefore not desirable for implementation in acoustic data transmissionsystems of the present invention. Thus, an embodiment of the presentinvention provides a solution to the above-mentioned carrier frequencyinstability problem changing the PSK signal structure, withoutcomplicating the acoustic transmitter and with few additions to theacoustic receiver.

(2) Acoustic Data Transmission Based on Two Types of DPSK

Embodiments of the present invention include an acoustic datatransmission system based on two types of DPSK techniques: (i) D¹PSK,the first order DPSK, modulates the first finite differences of thecarrier phase in the acoustic transmitter; and (ii) D²PSK, the secondorder DPSK, modulates the second finite differences of the carrier phasein the acoustic transmitter. At the receiving site, the acousticreceiver does not use any carrier recovery techniques or adaptivefrequency/phase adjustment procedures, but rather is based on directcalculation of current carrier phase (i.e., as it is in the acousticchannel).

Advantageously, these embodiments of the present invention aresubstantially independent of carrier phase offset (i.e., substantiallyinvariant to the initial phase shift in the acoustic system) at bothD¹PSK and D²PSK. In addition, these embodiments include a two-modetransmitter (D¹PSK or D²PSK) based on a simple universal differentialencoder and conventional carrier phase modulator. Moreover, theseembodiments include a D²PSK receiver, providing both D′PSK and D²PSKsignal processing, based on a simple double-differential autocorrelationdecoder with only symbol synchronization and without any carriersynchronization.

FIGS. 25 and 26 depict block diagrams respectively illustrating atransmission path and a receive path of an acoustic transmission systemthat uses two types of DPSK according to an embodiment of the presentinvention. The transmission path of FIG. 25 may be implemented iningestible capsule 104 and the receive path of FIG. 26 may implementedin an external receiver patch, such as sensor link module 602.

Referring to FIG. 25, the transmission path includes a firstdifferential encoder 2510, a second differential encoder 2520, amultiplier 2530, a carrier generator 2540, and an acoustic transducer/Tx2516. First differential encoder 2510 includes a multiplier 2512 and a(one bit) delay element 2514. In this scheme, a current data bit b_(k)in form of ±1 is multiplied by a result of a previous multiplicatione_(k−1) after it goes through delay element 2514. Thus, the encoded bite_(k) from first differential encoder 2510 can be written ase _(k) =e _(k−1) *b _(k)  (Eq. 3)

Second differential encoder 2520 includes a multiplier 2522 and a(one-bit) delay element 2524. The encoded bit e_(k) from firstdifferential encoder 2510 is multiplied by a result of a previousmultiplication f_(k−1) after it goes through delay element 2524. Thus,the encoded bit f_(k) from second differential encoder 2520 can bewritten asf _(k) =f _(k−1) *e _(k)  (Eq. 4)

The encoded bit from second differential encoder 2520 is then providedto multiplier 2530.

Multiplier 2530 multiplies the encoded bit from second differentialencoder 2520 with the signal from carrier generator 2540. The signalfrom multiplier 2530 is fed to acoustic transducer/Tx 2516.

Acoustic transducer/Tx 2516 converts the received signal into anacoustic signal that is transmitted through the multi-path acousticchannel.

After traveling through the multi-path acoustic channel, the acousticsignal is received by the receive path of FIG. 26. The receive pathincludes an acoustic transducer/Rx 2660, a double-differentialautocorrelation decoder 2666, a synch 2670, and a decision module 2676.Acoustic transducer/Rx 2660 receives the acoustic signal and converts itinto an electrical signal. Decoder 2666 directly calculates cos/sintrigonometric functions (I/Q components) of the first and second orderphase differences for the received signal (modulated carrier) in awell-known manner. The received signal from the output of acoustictransducer/Rx 2660 is fed to decoder 2666 and to synch 2670. I/Qcomponents from the output of decoder 2666 are fed to decision module2676 for making a decision regarding the transmitted data symbol.Decoder 2666 and decision module 2676 are controlled by synch 2670.

It is to be appreciated that the acoustic transmission systemillustrated in FIGS. 25 and 26 is presented for illustrative purposesonly, and not limitation. For example, other embodiments may include anacoustic data transmission system with a quadrature DPSK modulationscheme (D¹QPSK and D²QPSK). Such embodiments include a correspondingacoustic transmitter and receiver as would be apparent from thedescription contained herein. Additional embodiments may include asimple structure of a preamble signal, providing initial detection andsynchronization for the data transmission session, as well as phaseinitialization for both D¹PSK and D²PSK modes. Further embodiments usethe trigonometric functions of the first and second order phasedifferences at the outputs of the autocorrelation demodulator forestimation of characteristics of current movement and location ofingestible capsule 104.

Thus, an embodiment of the present invention uses two types of DPSKencoding to provide an efficient solution for carrier phase uncertaintyand carrier frequency instability in acoustic data transmission systems.These embodiments are substantially independent of carrier phase offsetand of carrier frequency offset (substantially invariant to phase andfrequency shifts in the acoustic channel). Also, these embodimentsprovide a high level of data transmission robustness (e.g., a highsignal-to-noise ratio), associated with the PSK modulation technique.

(iv) Example Acoustic Data Transmission within Human Body

FIGS. 22 and 23 depict block diagrams respectively illustrating atransmission path and a receive path of an acoustic data transmissionsystem for acoustically transmitting data through a human's bodyaccording to an embodiment of the present invention. The transmissionpath of FIG. 22 may be implemented in ingestible capsule 104 and thereceive path of FIG. 23 may be implemented in an external computingdevice, such as sensor link module 602. The acoustic transmission systemillustrated in FIGS. 22 and 23 is based on a DBPSK modulation scheme incombination with an 11-element Barker code (11-Barker). For illustrativepurposes, the acoustic transmission system of FIGS. 22 and 23 isdescribed below in terms of data transmission having a bit rate of 10kbit/s at 1 MHz carrier frequency through the acoustic channel withapproximately 100 μs pulse response.

Referring to FIG. 22, the transmission path includes a DBPSK encoder2200, a multiplier 2206, an 11-Barker register 2208, a carrier generator2213, and an acoustic transducer/Tx 2216. The DBPSK encoder includes amultiplier 2202 and a (one-bit) delay element 2204. The DBPSK encoderfunctions in a similar manner to multiplier 2002 and delay element 2004described above with reference to FIG. 20. For example, data bits in theform of ±1 with a bit rate of 10 kbit/s are fed to the input of theDBPSK encoder. The DBPSK includes multiplier 2202 and delay element2204, which has a delay of approximately T=100 μs. Each current bit ismultiplied by a result of the previous multiplication, as describedabove.

Barker register 2208 provides a Barker spreading code. The current ±1signal (with duration 100 μs at the output of multiplier 2206) istransformed into a wideband sequence of positive and negative ones (eachhaving a duration of approximately 100/11≈9.1 μs) by multiplication withthe Barker sequence (generated by Barker register 2208). Barker register2208 is an 11-bit cyclic shift register, containing ±1 binary digits asillustrated in FIG. 22. Barker register 2208 provides bit cyclicshifting with frequency 110 kHz, and therefore exactly 11 Barkerelements are within the 100 μs data symbol interval. Barker register2208 is synchronized with the data bit interval.

Carrier generator 2213 provides a 1 MHz carrier. The spreaded signalfrom the output of multiplier 2206, containing 11 positive and negativeones, modulates the 1 MHz carrier in multiplier 2222. The bit intervalcontains 100 cycles of the carrier, and Barker register 2208 containsabout 9 carrier cycles.

The modulated carrier from multiplier 2222 is fed into acoustictransducer/Tx 2216. Acoustic transducer/Tx 2216 transmits an acousticsignal into the multi-path acoustic channel within human 102.

After traveling through the multi-path acoustic channel, the acousticsignal is received by the receive path of FIG. 23. The receive pathincludes an acoustic transducer/Rx 2360, an 11-Barker register 2342, afirst band-pass filter 2352 and a second band-pass filter 2356, anautocorrelation DBPSK demodulator 2359, and a synch unit 2343.

Acoustic transducer/Rx 2360 receives the acoustic signal and transformsit into an electrical signal. The received signal from the output oftransducer/Rx 2360 first passes through first band pass filter 2352.First band pass filter 2352 includes a wideband filter BPF₁ with abandwidth of about 110 kHz around the 1 MHz carrier frequency.

The filtered signal is then multiplied, in multiplier 2341, by theBarker code from 11-Barker register 2342. 11-Barker register 2342functions in a similar manner to Barker register 2208 (FIG. 22)described above.

The convoluted signal from the output of multiplier 2341 passes throughsecond band pass filter 2356. Second band pass filter 2356 includes anarrowband filter BPF₂ with a bandwidth of about 10 kHz around the 1 MHzcarrier frequency. The signal is then fed into the autocorrelationdemodulator 2309.

Autocorrelation demodulator 2309 includes a delay element 2358, amultiplier 2354, an integrator 2352, and a sign detector (Sgn) 2380.Delay element 2358 has a time delay of approximately T=100 μs. It shouldbe noted that delay element 2358 of FIG. 23 differs from delay element2204 of FIG. 22. In the DBPSK encoder of FIG. 22, delay element 2204functions as a bit memory; whereas, in the autocorrelation demodulatorof FIG. 23, delay element 2358 functions as a delay line (samplesmemory).

In an embodiment, autocorrelation demodulator 2309 operates in thefollowing manner. Multiplier 2354 multiplies the current input signalwith the 100 μs delayed signal from delay element 2358. Integrator 2352integrates (accumulates) the product during bit interval T=100 μs.

Sgn 2380 determines the received bit based on the sign of the integral.For example, a positive sign (“+”) corresponds to a bit value of 1, anda negative sign (“−”) corresponds to a bit value of 0.

Importantly, the above-described demodulation scheme does not requiregeneration of the carrier and does not require any reference signal atall. Rather, the above-described demodulation scheme uses an initialsynchronization of Barker register 2342 and the current symbolsynchronization of both Barker register 2342 and integrator 2352 in theautocorrelation demodulator. At the ideal synchronization in theadditive white Gaussian noise (AWGN) channel the demodulator provides aBER=10⁻³ at SNR≈8.5 dB.

In an embodiment, a special preamble can be used for initialsynchronization of Barker register 2342. The preamble, which contains atleast two Barker sequences, is followed by a data package. During datapackage transmission, the symbol synchronization is carried out by synchunit 2343, using signals from the output of the demodulator.

(v) Improved Signal-to-Noise Ratio Based on Multi-Path Acoustic Signals

An embodiment of the present invention distinguishes different reflectedacoustic rays to extract the ray with a high signal-to-noise ratio(SNR). This embodiment uses nearly all reflected acoustic rays by (i)initially distinguishing the acoustic rays having different time delays,(ii) accumulating signals of the acoustic rays in space dividedreceivers, and (iii) making a final decision based on a combined(integral) signal of the space divided receivers. The improved SNR canbe achieved by a plurality of receive paths as illustrated in FIG. 24which receive an acoustic signal after it travels through a multi-pathacoustic channel. The acoustic signal can be transmitted through themulti-path acoustic channel using a transmitter similar to thosedescribed herein.

Referring to FIG. 24, the plurality of receive paths include an acoustictransducer/Rx 2460, a plurality of SCGs generating shifted versions ofthe spreading code, a corresponding plurality of demodulators, aplurality of SNR estimators, a plurality of weighted accumulators of thedemodulator's outputs, a decision block (integrator) 2470, and a synchunit 2465. As illustrated in FIG. 24, the plurality of SCGs include aSCG₁ 2421, a SCG₂ 2422, and a SCG_(N) 2423; the plurality ofdemodulators include a demodulator₁ 2431, a demodulator₂ 2432, and ademodulator_(N) 2433; the plurality of SNR estimators include a SNRestimator 2451, a SNR estimator 2452 and a SNR estimator 2453. Eachreceive path of FIG. 24 includes a SCG, a demodulator, and SNRestimator. For simplicity of exposition, the operation of SCG₁ 2421,demodulator₁ 2431, and SNR estimator 2451 is described below. Theoperation of the other SCGs, demodulators, and SNR estimators will beapparent from this description.

Acoustic transducer/Rx 2460 receives the acoustic signal after ittravels through the multi-path acoustic channel. Multiplier 2411multiplies the received signal from the output of acoustic transducer/Rx2460 by the shifted signals from the output of SCG 2421, and providesthe result to demodulator₁ 2431.

SNR estimator 2451 estimates the SNR of the received acoustic signal.Multiplier 2441 multiplies the soft decisions from the output ofdemodulator₁ 2431 by the weight coefficient w₁ provided by SNR estimator2451, and provides the result to integrator 2470.

Integrator 2470 combines the final signal from each receive path formaking a hard decision regarding the transmitted data symbol. The SCGsand the demodulators are controlled by synch unit 2465 in a similarmanner to that described above.

The plurality of receive paths of FIG. 24 combine a plurality ofreflected rays in the multi-path acoustic channel to provide an outputsignal having a high SNR, thereby providing improved performance.

Another embodiment combines the received data signal from each of aplurality of receivers (e.g. sensor link modules 602) having spacediversity. The plurality of spatially diverse receivers can be used indifferent manners. According to a first approach, the final (integral)signal from each spatially diverse receiver (as described above withreference to FIG. 24) is combined (with corresponding weightedcoefficients) into a super-signal, which serves as a basis for harddecision making. This approach provides a very high performance gain. Asecond approach provides signal processing in each spatially diversereceiver with only (individual) shift of the spreading code, and afterthat the outputs of the spatially diverse receivers are combined (withcorresponding weighted coefficients) into a final (integral) signal forhard decision making. According to a third approach, the individualreceivers find out in turn (in order of priority) the biggest nextreflection and use a combination of the found reflections for making thefinal hard decision.

It is important to note that the exemplary frequency band of operationaround 1 MHz is presented for illustrative purposes only, and notlimitation. Persons skilled in the relevant art(s) will appreciate thata higher data rate, for example 2 times illustrated above, can berealized based on the teachings above, translated into, for example, a 2MHz frequency band of operation. Such deviations from the teachingsabove are contemplated within the spirit and scope of this invention.

Furthermore, higher data rates may be achieved in accordance with anembodiment of the present invention by operating multiple parallel datapaths or a single data path split into multiple data paths, wherein eachis or many data paths are implemented through the methods described andexemplified above and operational on discrete and disjoint frequencybands. For example, from teachings and examples above, and withreference to FIG. 9, transducer 904A may be operational at 1 MHz, with abandwidth of 100 kHz, and a data rate of 10 kbps. Additionally,transducer 904B may operate at 1.2 MHz, with 100 kHz of bandwidth and 10kbps data rate. Device 104, if operating transducers 904A and 904Bconcurrently, can achieve a data rate of 20 kbps to an external set ofreceivers. A person skilled in the relevant art(s) will appreciate howto design a system with a plurality of transmitters and receivers inparallel operation to achieve a targeted data bit rate without departfrom the spirit and scope of this present invention. For example, aplurality of orthogonal spreading codes may be used in combination witha single acoustic transducer to transmit through a correspondingplurality of acoustic channels, thereby increasing the data rate oftransmission.

C. Frequency Hopping

i. Overview

FIG. 27 illustrates a frequency hopping (FH) scheme to encode and/ordecode an acoustic communication signal according to an exemplaryembodiment of the present invention. An acoustic communication signal2700, such as communication signal 106, may be transmitted from atransmitter, such as ingestible capsule 104, to a receiver, such asexternal computing device 108 or one or more sensor link modules 602attached to the skin of the body, using the FH scheme. The FH schemeencodes and/or decodes communication signals by switching a carrierfrequency among one or more frequency channels. The carrier frequencyused to encode and/or decode the acoustic communication signal ischanged or hopped over a range of frequencies according to a chosen codeknown as a hopping pattern.

As shown in FIG. 27, an acoustic communication signal 2700 may bepartitioned into one or more time intervals denoted as t₁ through t_(N).Time intervals t₁ through t_(N) may represent the duration of a bit, abyte, a symbol, a session, or any other suitable time interval that willbe apparent to those skilled in the relevant art. Each time interval t₁through t_(N) includes a corresponding frequency channel denoted as ch₁through ch_(N). In an exemplary embodiment, an initialization frequencychannel, such as frequency channel ch₁, is reserved as a data sequenceinitiation signal or a synchronization signal between the transmitterand the receiver. After transmission of the acoustic communicationsignal, the transmitter transmits the initialization frequency channelto allow for transmission of a next acoustic communication signal. Upondetection of the initialization frequency channel, the receiver switchesa corresponding carrier frequency to a carrier frequency associated withthe initial frequency channel to begin decoding of the next acousticcommunication signal.

The FH scheme selects or switches among frequency channels ch₁ throughch_(N) based upon time intervals t₁ through t_(N) to encode and/ordecode acoustic communication signal 2700. For example, frequencychannel ch₁ is selected for time interval t₁. After time interval t₁lapses or expires, frequency channel ch₂ is selected for time intervalt₂. The transition between a first frequency channel, such as frequencychannel ch₁ and a second frequency channel, such as frequency channelch₂, may be substantially instantaneous, as shown in FIG. 27, ordelayed. Likewise, as time interval t₂ expires, frequency channel ch₃ isselected for time interval t₃. Each of remaining frequency channels ch₄through ch_(N) is selected for a corresponding time interval t₄ throught_(N) in a similar manner. Upon expiration of time interval t_(N),frequency channel ch₁ is selected once again to continue switching amongfrequency channels ch₁ through ch_(N) based upon time intervals t₁through t_(N).

In an exemplary embodiment, a maximum duration of time intervals t₁through t_(N) is such that the information content embedded with acorresponding frequency channel is transmitted and/or received beforethe acoustic multipath phenomena generates a second considerableresidual ray, described previously as the clear channel, for thatparticular frequency in a target environment, such as human 102. Thesecond considerable ray represents the first reflection of thetransmitted communication signal generated by the multipath phenomena,and starts the time period of a transitionary channel. In this exemplaryembodiment, the duration (T) for each time interval t₁ through t_(N) maybe given by:

$\begin{matrix}{{T = \frac{T_{RAY}}{NUM\_ CH}},} & \left( {{Eq}.\mspace{14mu} 5} \right)\end{matrix}$where T_(RAY) represents a truncated ray delay and NUM_CH represents thenumber of frequency channels in frequency channels ch₁ through ch_(N).The truncated ray delay represents an amount of time necessary for allrays generated by the multipath phenomena for a corresponding frequencyto be attenuated to a negligible level, such as, but not limited to,fifteen decibels (dB) to provide an example. In an exemplary embodimentsuitable for use in human 102 and at a particular ultrasonic frequencyrange, the truncated ray delay may be, for example, approximately equalto from 100 to 200 microseconds. However, this example is not limiting,and other maximum durations for time intervals t₁ through t_(N) that areapparent to those skilled in the relevant art are within the scope andspirit of the present invention.

From the discussion above, the multipath phenomena may cause acousticcommunication signal 2700 to reach the receiver by one or more paths.Switching from a frequency channel, such as frequency channel ch₁, toanother frequency channel, such as frequency channel ch₂, beforegeneration of the second considerable ray mitigates the effects of themultipath phenomena. In addition, cyclic repetition of frequencychannels ch₁ through ch_(N) after at least T*NUM_CH seconds, allows thetransmitter and/or the receiver to reuse frequency channels ch₁ throughch_(N) after all considerable rays from a corresponding frequencychannel ch₁ through ch_(N) have become negligible, returning thefrequency of interest to a clear channel status. For example, thetransmitter may once again select the corresponding carrier frequencyassociated with frequency channel ch₁ after at least T*NUM_CH secondshas elapsed to allow the second considerable residual ray and all otherconsiderable rays to attenuate to a negligible level.

FIG. 28 illustrates a hopping pattern used to encode and/or decode theacoustic communication signal according to an exemplary embodiment ofthe present invention. The hopping pattern may be represented by atime-frequency matrix. The time-frequency matrix is a graphicalrepresentation of carrier frequencies, denoted as f₁ through f_(M), thatmay be assigned to a corresponding frequency channel ch₁ through ch_(N).Each frequency channel in frequency channel ch₁ through ch_(N) need notcontain a corresponding carrier frequency. For example, carrierfrequency f₁ may be assigned to frequency channel ch₁. In other words,carrier frequency f₁ is used for the encoding and/or decoding of theacoustic communication signal during the time interval t₁ correspondingto frequency channel ch₁. Likewise, carrier frequency f_(M) may beassigned to frequency channel ch₂. Similarly, carrier frequency f₃ maybe assigned to frequency channel ch₃. Finally, carrier frequency f₃ maybe assigned to frequency channel ch_(N). However, this example is notlimiting, those skilled in the arts will recognize that frequencychannels ch₁ through ch_(N) may assigned to any other suitable sequenceof carrier frequencies f₁ through f_(M) without departing from thespirit and scope of the invention. For example, any suitable random orpseudo-random sequence may be used to assign carrier frequencies f₁through f_(M) to the corresponding frequency channel ch₁ through ch_(N).As another example, carrier frequencies f₁ through f_(M) may be assignedto the corresponding frequency channel ch₁ through ch_(N) in asequential manner with a carrier frequency having a least frequencybeing assigned to frequency channel ch₁ and a carrier frequency having agreatest frequency being assigned to frequency channel ch_(N). In afurther example, an identification of the transmitter and/or thereceiver, such as but not limited to an electronic identification, maybe used to assign carrier frequencies f₁ through f_(M) to thecorresponding frequency channel ch₁ through ch_(N). In this example, theidentification of the transmitter and/or the receiver is unique for eachtransmitter and/or receiver thereby encrypting the acousticcommunication signal based on the hopping pattern. A further example ishaving no frequency used more than once in channels ch₁ through ch_(N)to ensure that each frequency has a clear channel. Furthermore, in anembodiment using encrypted information, a transmitter may send a signalon a frequency that is not part of the matrix. This additionalinformation intentionally obscures the real information.

ii. Combination of Frequency Hopping and Pulse Interval Encoding

FIG. 29A illustrates a combined FH and pulse interval encoding (PIE)scheme to encode and/or decode an acoustic communication signalaccording to an exemplary embodiment of the present invention. Anacoustic communication signal 2900 may represent an exemplary embodimentof communication signal 106. From the discussion of FIG. 27 above, atransmitter, such as communications module 204, transmits acousticcommunication signal 2900 by encoding an information signal, such assensor output signal 212, onto frequency channels ch₁ through ch_(N)corresponding to time intervals t₁ through t_(N). The transmitter delaysthe transmission of adjacent frequency channels, such as frequencychannel ch₁ and frequency channel ch₂, by a corresponding time delay T₁through T_(N) to encode the information signal.

As shown in FIG. 29A, the transmitter transmits a first frequencychannel, such as frequency channel ch₁, for a first interval of time,such as time interval t₁. The transmitter then waits or ceases totransmit for a corresponding time delay, such as time delay T₁, to beginthe transmission of a second frequency channel, such as frequencychannel ch₂. The transmitter encodes the information signal by varying alength of the corresponding time delay T₁. More specifically, thetransmitter encodes the information signal by delaying the transmissionof the second frequency channel a number of delay intervals i₁ throughi_(k). The number of delay intervals i₁ through i_(k) included within acorresponding time delay T₁ through T_(N) represents a logic value. Thelogic value may be one or more bits, one or more bytes, one or moresymbols, or any other suitable data length or combination of datalengths. An individual delay interval in delay intervals i₁ throughi_(k) may be a duration of one or more bits, one or more bytes, one ormore symbols, or any other suitable data length or combination of datalengths. An advantage of encoding using the scheme of FIG. 29A is thatall actual transmit time i₁ can be as minimal as possible while the dataencoding may extend a period of no transmission T₁. The average dutycycle of the transmitter emission may then fall substantially below 50%,which is a typical goal in most low power transmission systems. Sincereasonable power is consumed when the transmitter is emitting, thisencoding scheme is ultimately extremely power efficient from thestandpoint of the transmitter.

As shown in FIG. 29B, delaying a transmission of a second frequencychannel ch_(B) after a transmission of a first frequency channel ch_(A)by delay interval i₁ may represent a first logic value, such as a binaryzero-zero. A second logic value, such as a binary one-zero, may berepresented by delaying the transmission of second frequency channelch_(B) after the transmission of first frequency channel ch_(A) by acombined duration of delay interval i₁ through delay interval i₂. Athird logic value, such as a binary one-one, may be represented bydelaying the transmission of second frequency channel ch_(B) after thetransmission of first frequency channel ch_(A) by a combined duration ofdelay interval i₁ through delay interval i₃. A fourth logic value, suchas a binary zero-one, may be represented by delaying the transmission ofsecond frequency channel ch_(B) after the transmission of firstfrequency channel ch_(A) by a combined duration of delay interval i₁through delay interval i₄. However, this example is not limiting, thoseskilled in the arts will recognize that any logic value may berepresented by delaying the transmission of second frequency channelch_(B) any number of delay intervals i₁ through i_(k) without departingfrom the spirit and scope of the invention. For example, N logic valuesmay be represented by delaying the transmission of second frequencychannel ch_(B) any suitable number of delay intervals i₁ through i_(N)and/or combinations thereof.

In a particular embodiment, relevant to a low power and reasonablycompact sensor device 104, a timing basis may be derived from a simpleand non-accurate on-board clock. Simple, low power clocks tend to driftfrom a target frequency for a variety of reasons and conditionsunderstandable to one of skill in the art. The drift is more severe thelonger the time period from synchronization. An effective and efficientdesign for the embodiment of FIG. 29B in this case may maintain aminimal time period i₁, while increasing the time periods i₂, i₃, and soon to compensate for anticipated maximal drift.

A receiver, such as external computing device 108 or one or more sensorlink modules 602 attached to the skin of the body, decodes acousticcommunication signal 2900 to recover the information signal. Inparticular, the receiver detects first frequency channel ch_(A) thenmeasures a length of the corresponding time delay T₁ through T_(N) untildetection of second frequency channel ch_(B). The receiver assigns arecovered logic value based upon the length of the corresponding timedelay T₁ through T_(N). More specifically, the receiver measures thenumber of delay intervals i₁ through i_(k) to determine the length ofthe corresponding time delay T₁ through T_(N), then assigns the logicvalue to a recovered information signal to recover the informationsignal based upon the length of the corresponding time delay T₁ throughT_(N).

To decode acoustic communication signal 2900 encoded according to FIG.29B, the receiver assigns the first logic value to the recoveredinformation signal when a time delay between first frequency channelch_(A) and second frequency channel ch_(B) is measured as delay intervali₁. Likewise, if the receiver measures the time delay between firstfrequency channel ch_(A) and second frequency channel ch_(B) as thecombined duration of delay interval i₁ through delay interval i₂, thereceiver assigns the second logic value to the recovered informationsignal. Similarly, if the receiver measures the time delay between firstfrequency channel ch_(A) and second frequency channel ch_(B) as thecombined duration of delay interval i₁ through delay interval i₃, thereceiver assigns the third logic value to the recovered informationsignal. Finally, if the receiver measures the time delay between firstfrequency channel ch_(A) and second frequency channel ch_(B) as thecombined duration of delay interval i₁ through delay interval i₄, thereceiver assigns the fourth logic value to the recovered informationsignal. However, this example is not limiting, those skilled in the artswill recognize that any logic value may be assigned to the recoveredinformation signal based upon any suitable combination of delayintervals i₁ through i_(K) without departing from the spirit and scopeof the invention. For example, N logic values may be assigned to therecovered information signal using any suitable number of delayintervals i₁ through i_(K) and/or combinations thereof.

iii. Combination of Frequency Hopping and Differential Phase ShiftKeying

FIG. 30A illustrates a combined FH and differential phase shift keying(DPSK) scheme to encode and/or decode an acoustic communication signalaccording to an exemplary embodiment of the present invention. From thediscussion of FIG. 27 above, a transmitter, such as communicationsmodule 204, transmits an acoustic communication signal 3000, such ascommunication signal 106, by encoding an information signal, such assensor output signal 212, onto frequency channels ch₁ through ch_(N)corresponding to time intervals t₁ through t_(N). The transmitter embedsone or more phases, denoted as ω₁ through ω_(i), of a correspondingcarrier frequency, such as carrier frequencies f₁ through f_(M) asdiscussed in FIG. 28, onto each frequency channel in frequency channelsch₁ through ch_(N) to encode the information signal. In other words,transitions among one or more phases ω₁ through ω_(i) within acorresponding frequency channel in frequency channels ch₁ through ch_(N)are used to encode the information signal.

Phases ω₁ through ω_(i) are relative to the preceding phase. Suchsystems, as would be expected in very low power devices such as withsensor device 104, do not have extremely stable oscillators and maydrift, have phase distortions, etc. Therefore, a phase reference to aninitial phase, running for many bit periods and phase changes is verydifficult to build. An encoding scheme that is simpler to implement in alow power scenario involving a phase change from a first time period t₁to a second time period t₂, another phase change from a time period t₂to a third time period t₃, and so on as is referred to herein as adifferential phase change. FIG. 30B depicts two cycles of frequencies.Depending upon design goals and available bandwidths for operation, moreor fewer cycles may be used as necessary as would be understood by aperson skilled in the art. Thus, use of any number of cycles offrequencies in between phase changes does not depart from the spirit andscope of this invention.

As shown in FIG. 30A, the transmitter transmits a carrier frequencyhaving the one or more phases ω₁ through ω_(i), such as one of carrierfrequencies f₁ through f_(M) as shown in FIG. 28, associated with afirst frequency channel, such as frequency channel ch₁, for a firstinterval of time, such as time interval t₁. The transmitter encodes theinformation signal by transmitting the one or more phases ω₁ throughω_(i) of the carrier frequency throughout the first interval of time.After the first interval of time lapses or expires, the transmittercycles through frequency channels ch₁ through ch_(N) as discussed inFIG. 27 and transmits the one or more phases ω₁ through ω_(i) of thecarrier frequency associated with frequency channels ch₁ through ch_(N),as discussed in FIG. 28 to encode the information signal.

As shown in FIG. 30B, the transmitter transmits a first phase ω₁ of acarrier frequency, such as carrier frequencies f₁ through f_(M),associated with frequency channels ch₁ through ch_(N), for a timeinterval t_(A), a time interval t_(B), and a time interval t_(C) torepresent a first logic value, such as a binary zero-zero. A combinationof time interval t_(A), time interval t_(B), and time interval t_(C) issubstantially less than or equal to one or more of time intervals t₁through t_(N). A second logic value, such as a binary zero-one, may berepresented by transmitting the first phase ω₁ of the carrier frequencyfor time interval t_(A) and time interval t_(B) followed by transmittinga second phase ω₂ of the carrier frequency for time interval t_(C). Athird logic value, such as a binary one-one, may be represented bytransmitting the first phase ω₁ of the carrier frequency for timeinterval t_(A), the second phase ω₂ of the carrier frequency for timeinterval t_(B), followed by the first phase ω₁ of the carrier frequencyfor time interval t_(C). A fourth logic value, such as a binaryone-zero, may be represented by transmitting the first phase ω₁ of thecarrier frequency for time interval t_(A), the second phase ω₂ of thecarrier frequency for time interval t_(B) and time interval t_(C).However, this example is not limiting, those skilled in the art willrecognize that the transmitter may encode the information signal torepresent any suitable number of logic values by transmitting at leastone of the one or more phases ω₁ through ω_(i) of the carrier frequencythroughout time intervals t₁ through t_(N). For example, the transmittermay encode the information signal using a carrier frequency having fourphase differences to generate a combined FH and differential quadraturephase shift keyed (DQPSK) acoustic communication signal, a carrierfrequency having eight phase differences to generate a combined FH anddifferential 8-phase shift keyed (D8PSK) acoustic communication signal,and/or a carrier frequency having N phase differences to generate acombined FH and differential N-phase shift keyed (DNPSK) acousticcommunication signal.

A receiver, such as external computing device 108 or one or more sensorlink modules 602 attached to the skin of the body, decodes acousticcommunication signal 3000 to recover the information signal. Inparticular, the receiver detects the one or more phases ω₁ through ω_(i)of the carrier frequency throughout time intervals t₁ through t_(N). Thereceiver assigns a recovered logic value based upon a number oftransitions among the one or more phases ω₁ through ω_(i) of the carrierfrequency.

To decode acoustic communication signal 3000 encoded according to FIG.30B, the receiver assigns the first logic value to the recoveredinformation signal upon detecting the first phase ω₁ of the carrierfrequency for time interval t_(A), time interval t_(B), and timeinterval t_(C). Likewise, if the receiver detects the first phase ω₁ ofthe carrier frequency for time interval t_(A) and time interval t_(B)followed by the second phase ω₂ of the carrier frequency for timeinterval t_(C), the receiver assigns the second logic value to therecovered information signal. Similarly, if the receiver detects thefirst phase ω₁ of the carrier frequency for time interval t_(A), thesecond phase ω₂ of the carrier frequency for time interval t_(B)followed by the first phase ω₁ of the carrier frequency for timeinterval t_(C), the receiver assigns the third logic value to therecovered information signal. Finally, if the receiver detects the firstphase ω₁ of the carrier frequency for time interval t_(A) followed bythe second phase ω₂ of the carrier frequency for time interval t_(B) andtime interval t_(C), the receiver assigns the fourth logic value to therecovered information signal. However, this example is not limiting,those skilled in the art will recognize that the receiver may decode theacoustic communication signal by assigning any suitable number of logicvalues by detecting at least one of the one or more phases ω₁ throughω_(i) of the carrier frequency throughout time intervals t₁ throught_(N).

FIG. 31 illustrates a block diagram of a transmitter to encode aninformation signal using a combined FH and DPSK scheme according to anexemplary embodiment of the present invention. A transmitter 3110 may beused to generate acoustic communication signal 3000 as shown in FIG.30A. Transmitter 3110 may represent an exemplary embodiment ofcommunications module 204. As will be understood by persons skilled inthe relevant art from the teachings provided herein, transmitter 3110may be readily implemented in hardware, software, or a combination ofhardware and software. For example, based on the teachings providedherein, a person skilled in the relevant art could implement transmitter3110 via a combination of one or more application specific integratedcircuits and a processor core for implementing software commands storedin one or more attached memories. However, this example is not limiting,and other implementations are within the scope and spirit of the presentinvention.

As shown in FIG. 31, transmitter 3110 may include an acousticcommunications module 3112 and a radiating element 3114. Acousticcommunications module 3112 includes an encoder 3100, a functiongenerator 3102, a mixer 3104, and a carrier generator 3106. Acousticcommunications module 3112 may represent an exemplary embodiment ofacoustic communications module 302. Encoder 3100 receives an informationsignal 3150. Information signal 3150 may include, but is not limited to,sensor output signal 212. Encoder 3100 encodes information signal 3150to generate a reference pulse 3154. In an exemplary embodiment, encoder3100 partitions information signal 3150 into one or more bits, one ormore bytes, one or more symbols, or any other suitable manner that willbe apparent to those skilled in the relevant art.

Function generator 3102 operates on reference pulse 3154 to produce anencoded baseband communication signal 3156. More specifically, functiongenerator 3102 operates upon reference pulse 3154 using one or moremathematical functions, such as a Walsh function or any other suitablemathematical function that will be apparent to those skilled in therelevant art. For example, for a one bit transmission, functiongenerator 3102 may store a first Walsh function S₁ and a second Walshfunction S₂. First Walsh function S₁ may be represented as:[S ₀ S ₀],  (Eq. 6)where S₀ is a reference pulse with any carrier frequency, such ascarrier frequencies f₁ through f_(M). In an exemplary embodiment,reference pulse 3154 represents reference pulse S₀. Likewise, secondWalsh function S₂ may be represented as:[S ₀ −S ₀].  (Eq. 7)

Function generator 3102 may output first Walsh function S₁ or secondWalsh function S₂ based upon reference pulse 3154. However, this exampleis not limiting, those skilled in the art will recognize that functiongenerator 3102 may operate upon reference pulse 3154 using one or moremathematical functions without departing from the spirit and scope ofthe invention. For example, a set of Walsh functions for a two bittransmission may be denoted as S₁=[S₀ S₀ S₀ S₀], S₂=[S₀ S₀ −S₀ −S₀],S₃=[S₀ −S₀ −S₀ S₀], and S₄=[S₀ −S₀ S₀ −S₀]. Likewise, a set of Walshfunctions for a three bit transmission may be denoted as S₁=[S₀ S₀ S₀ S₀S₀ S₀ S₀ S₀], S₂=[S₀ S₀ S₀ −S₀ −S₀ −S₀ −S₀−S₀], S₃=[S₀ S₀ −S₀ −S₀ −S₀−S₀ S₀ S₀], S₄=[S₀ S₀ −S₀ −S₀ S₀ S₀ −S₀ −S₀], S₅=[S₀ −S₀ −S₀ S₀ S₀ −S₀−S₀ S₀], S₆=[S₀ −S₀ −S₀ S₀−S₀ S₀ S₀ −S₀], S₇=[S₀ −S₀ S₀ −S₀ −S₀ S₀ −S₀S₀], and S₈=[S₀ −S₀ S₀ −S₀ S₀ −S₀ S₀ −S₀].

Carrier generator 3106 generates a carrier frequency 3160 according tothe FH scheme as discussed in conjunction with FIG. 27 and FIG. 28. Forexample, carrier generator 3106 generates carrier frequency 3160corresponding to carrier frequencies f₁ through f_(M) assigned tofrequency channels ch₁ through ch_(N).

Multiplier 3104 generates an electrical communication signal 3158 bymultiplying encoded baseband communication signal 3156 and carrierfrequency 3160. More specifically, multiplier 3104 upconverts encodedbaseband communication signal 3156 using carrier frequency 3160 togenerate electrical communication signal 3158.

Radiating element 3114 converts electrical communication signal 3158 toan acoustic representation to generate an acoustic communication signal3152. Acoustic communication signal 3152 is an exemplary embodiment of,but is not limited to, communication signal 106. Radiating element 3114may represent an exemplary embodiment of radiating element 304.Radiating element 3114 may be, but is not limited to, anelectromechanical transducer or piezoelectric (e.g., PZT, PVDF, etc.)element or transducer that vibrates at acoustic frequencies.

FIG. 32 illustrates a block diagram of a receiver to decode an acousticcommunication signal using a combined FH and DPSK scheme according to anexemplary embodiment of the present invention. A receiver 3200, such asexternal computing device 108 or one or more sensor link modules 602attached to the skin of the body, decodes an acoustic communicationsignal 3250 to recover a recovered information signal 3252. As shown inFIG. 32, receiver 3200 may include a radiating element 3202, a bandpassfilter array 3204, a demodulator 3206, a function generator 3208, and acarrier generator 3210.

Radiating element 3202 receives acoustic communication signal 3250, suchas acoustic communication signal 3000 to provide an example. Radiatingelement 3202 converts acoustic communication signal 3250 to anelectrical signal to generate an electrical communication signal 3254.Radiating element 3202 may be, but is not limited to, anelectromechanical transducer or piezoelectric (e.g., PZT, PVDF, etc.)element or transducer that vibrates at acoustic frequencies.

Bandpass filter array 3204 receives electrical communication signal 3254to generate a filtered communication signal 3256. Bandpass filter array3204 may include a selectable arrangement of one or more bandpassfilters. Each bandpass filter in bandpass filter array 3204 may beimplemented as, but not limited to, a Bessel filter, a Butterworthfilter, a Chebyshev filter, a Comb filter, an Elliptic filter, or anyother suitable filter topology to provide some examples. At least one ormore of the bandpass filters corresponds to one or more of frequencychannels ch₁ through ch_(N). In an exemplary embodiment, bandpass filterarray 3204 includes one bandpass filter for each of frequency channelsch₁ through ch_(N). For example, a bandpass filter array 3204 havingfive bandpass filters may filter an electrical representation ofacoustic communication signal 3250, namely electrical communicationsignal 3254, that is DPSK encoded over five frequency channels ch₁through ch₅.

Demodulator 3206 uses a carrier frequency 3260 to demodulate and/ordownconvert filtered communication signal 3256 to produce a demodulatedcommunication signal 3258. In an exemplary embodiment, demodulator 3206demodulates filtered communication signal 3256 to a baseband frequency.Demodulator 3206 may be implemented as an optimal non-coherentdemodulator, a suboptimal non-coherent demodulator, such as adelay-and-multiply receiver, or any other suitable demodulator capableof demodulating a DPSK, a DQPSK, a D8PSK, and/or a DNPSK encodedcommunication signal.

Carrier generator 3210 generates carrier frequency 3260 according to theFH scheme as discussed in conjunction with FIG. 27 and FIG. 28. Forexample, carrier generator 3208 generates carrier frequency 3260corresponding to carrier frequencies f₁ through f_(M) assigned tofrequency channels ch₁ through ch_(N).

Function generator 3208 receives demodulated communication signal 3258to generate recovered information signal 3252, such as communicationsignal 506 in FIG. 5. Function generator 3208 generates recoveredinformation signal 3252 by decoding demodulated communication signal3258 using one or more mathematical functions, such as a Walsh functionor any other suitable mathematical function to provide some examples.For example, for a one bit transmission, function generator 3208 mayoperate upon demodulated communication signal 3258 using first Walshfunction S₁ and assign a first logic value to recovered informationsignal 3252 corresponding to first Walsh function S₁. Similarly,function generator 3208 may operate upon demodulated communicationsignal 3258 using second Walsh function S₂ and assign a second logicvalue to recovered information signal 3252 corresponding to second Walshfunction S₂. Those skilled in the art will recognize that functiongenerator 3208 may assign recovered information signal 3252 any suitablenumber and/or type of logic values using one or more suitablemathematical functions. For example, function generator 3208 may assignrecovered information signal 3252 a first logic value, a second logicvalue, a third logic value and/or a fourth logic value corresponding tofirst Walsh function S₁, second Walsh function S₂, third Walsh functionS₃, and/or fourth Walsh function S₄ for a two bit transmission.

In an exemplary embodiment, receiver 3200 may simultaneously demodulateone or more acoustic communication signals 3250. Receiver 3200 maysimultaneously receive one or more acoustic communication signals 3250produced by one or more transmitters synchronously transmitting on asubstantially identical frequency band using orthogonal sets ofmathematical functions. For example, a first transmitter may use a firstmathematical function, such as a first Walsh function S₁ of [S₀ S₀ S₀S₀] and a second Walsh function S₂=[S₀ S₀ −S₀ −S₀] for its bittransmission while a second transmitter may use a second mathematicalfunction, such as a first Walsh function S₁ of [S₀ −S₀ −S₀ S₀] and asecond Walsh function S₂=[S₀ −S₀ S₀ −S₀] for its bit transmission.

iv. Combination of Frequency Hopping and Frequency Shift Keying

From the discussion of FIG. 27 above, a transmitter, such ascommunications module 204, may transmit an acoustic communicationsignal, such as communication signal 106, by encoding an informationsignal, such as sensor output signal 212, onto frequency channels ch₁through ch_(N) corresponding to time intervals t₁ through t_(N). Thetransmitter embeds one or more carrier frequencies, such as carrierfrequencies f₁ through f_(M), onto each frequency channel in frequencychannels ch₁ through ch_(N) to encode the information signal.

FIG. 33A illustrates a hopping pattern used to encode and/or decode anacoustic communication signal using a combination of FH and differentialfrequency shift keying (DFSK) according to an exemplary embodiment ofthe present invention. Carrier frequencies f₁ through f_(M) as discussedin FIG. 28, may be partitioned or divided into one or more sets ofcarrier frequencies. The one or more sets of carrier frequencies mayinclude one or more bands, registers, octaves, or any other suitabledivision of carrier frequencies f₁ through f_(M) that will be apparentto those skilled in the art. For example, as shown in FIG. 33A,frequency channels ch₁ through ch_(N) correspond to a first set ofcarrier frequencies f including carrier frequencies f₁ through f_(M/2)and a second set of carrier frequencies F including carrier frequenciesf_(M/2+1) through f_(M/2). However, this example is not limiting, thoseskilled in the arts will recognize that carrier frequencies f₁ throughf_(M) may be divided into one or more sets of carrier frequencieswithout departing from the spirit and scope of the invention. Thoseskilled in the arts will also recognize that the sets of carrierfrequencies, such as first set of carrier frequencies f and second setof carrier frequencies F, may contain a similar and/or a dissimilarnumber of carrier frequencies and consecutive and/or non-consecutivefrequencies without departing from the spirit and scope of theinvention.

Referring back to FIG. 33A, the transmitter and/or the receiver mayassign one or more carrier frequencies to frequency channels ch₁ throughch_(N). For example, the transmitter and/or the receiver may assigncarrier frequency f₁ and/or carrier frequency f_(M/2+1) to frequencychannel ch₁. Likewise, the transmitter and/or the receiver may assigncarrier frequency f_(M/2) and/or carrier frequency f_(M) to frequencychannel ch₂. Similarly, the transmitter and/or the receiver may assigncarrier frequency f₃ and/or carrier frequency f_(M/2+3) to frequencychannel ch₃. Finally, the transmitter and/or the receiver may assigncarrier frequency f₃ and/or carrier frequency f_(M/2+3) to frequencychannel ch_(N). However, this example is not limiting, those skilled inthe arts will recognize that frequency channels ch₁ through ch_(N) maybe assigned to any other suitable sequence of carrier frequencies f₁through f_(M) without departing from the spirit and scope of theinvention. Furthermore, to ensure a frequency always has a clearchannel, the frequencies can be assigned to the channels so that nofrequency is used more than once.

FIG. 33B further illustrates the hopping pattern used to encode and/ordecode the acoustic communication signal using the combination of FH andDFSK according to an exemplary embodiment of the present invention. Inthis exemplary embodiment, carrier frequencies f₁ through f_(M) arepartitioned or divided evenly into two sets of carrier frequencies.Carrier frequencies f₁ through f_((M/2)) form a first set of carrierfrequencies f. Carrier frequencies f_((M/2+1)) through f_(M) form asecond set of carrier frequencies F. In an exemplary embodiment, carrierfrequencies f₁ through f_((M/2)) are substantially less than or equal tocarrier frequencies f_((M/2+1)) through f_(M). However, this example isnot limiting, those skilled in the arts will recognize that frequencychannels ch₁ through ch_(N) may be assigned to one or more sets ofcarrier frequencies using any other suitable sequence of carrierfrequencies f₁ through f_(M) without departing from the spirit and scopeof the invention.

As shown in FIG. 33B, first set of carrier frequencies f may be storedin a first set of slots of a data register. Those skilled in the artwill recognize that the functionality of the data register may beimplemented using other suitable classes of storage media such as avolatile memory, for example a read-only memory (ROM), a non-volatilememory, such as a random access memory (RAM), or any other devicecapable of storing data without departing from the spirit and scope ofthe invention. Likewise, second set of carrier frequencies F may bestored in a second set of slots of the data register. The data registermay be implemented as a processor register, a hardware register, or anyother suitable category of storage area. In addition, the data registermay be implemented as, but is not limited to, a general purpose register(GPR) to store both data and addresses, a floating point register (FPR)to store floating point numbers, a constant register to hold read-onlyvalues, a vector register to hold data for vector processing done bySingle Instruction, Multiple Data (SIMD) instructions, a specialfunction register, or any other suitable class of registers depending onthe content of the data. The data register may be implemented as aregister file, individual flip-flops, high speed core memory, thin filmmemory, and any other suitable implementation that will be apparent tothose skilled in the art.

The transmitter selects between first set of carrier frequencies f andsecond set of carrier frequencies F for each frequency channel infrequency channels ch₁ through ch_(N) to encode the information signal.In other words, transitions among first set of carrier frequencies f andsecond set of carrier frequencies F encode the information signal. Asshown in FIG. 33C, the transmitter transmits a carrier frequency fromfirst set of carrier frequencies f for a time interval t_(AA), a timeinterval t_(BB), and a time interval t_(CC) to represent a first logicvalue, such as a binary zero-zero. As used herein, the term “logicvalue” also refers to symbols belonging to sets of indeterminate size,not only to sets having just two states. Time interval t_(AA), timeinterval t_(BB), and time interval t_(CC) are substantially equal to acorresponding time interval t₁ through t_(N) corresponding to frequencychannels ch₁ through ch_(N) as discussed in FIG. 27. Alternately, thetransmitter transmits a carrier frequency from second set of carrierfrequencies F for a time interval t_(AA), a time interval t_(BB), and atime interval t_(CC) to represent the first logic value.

A second logic value, such as a binary zero-one, may be represented bytransmitting the carrier from first set of carrier frequencies f fortime interval t_(AA) and time interval t_(BB) followed by the carrierfrequency from second set of carrier frequencies F for time intervalt_(CC). Alternately, the second logic value may be represented bytransmitting the carrier frequency from second set of carrierfrequencies F for time interval t_(AA) and time interval t_(BB),followed by the carrier frequency from first set of carrier frequenciesf for time interval t_(CC).

A third logic value, such as a binary one-zero, may be represented bytransmitting the carrier frequency from second set of carrierfrequencies F for time interval t_(AA) and time interval t_(BB) followedby the carrier frequency from first set of carrier frequencies f fortime interval t_(CC). Alternately, the third logic value may berepresented by transmitting the carrier frequency from first set ofcarrier frequencies f for time interval t_(AA) and time interval t_(BB),followed by the carrier frequency from second set of carrier frequenciesF for time interval t_(CC).

A fourth logic value, such as a binary one-one, may be represented bytransmitting the carrier frequency from first set of carrier frequenciesf for time interval t_(AA), the carrier frequency from second set ofcarrier frequencies F for time interval t_(BB), followed by the carrierfrequency from first set of carrier frequencies f for time intervalt_(CC). Alternately, the fourth logic value may be represented bytransmitting the carrier frequency from second set of carrierfrequencies F for time interval t_(AA), the carrier frequency from firstset of carrier frequencies f for time interval t_(BB), followed by thecarrier frequency from second set of carrier frequencies F for timeinterval t_(CC). However, this example is not limiting, those skilled inthe art will recognize that the transmitter may encode the informationsignal to represent any suitable number of logic values by transmittingany suitable number of carrier frequencies from one or more sets ofcarrier frequencies without departing from the spirit and scope of theinvention. For example, the transmitter may encode the informationsignal using four sets of carrier frequencies to generate a combined FHand differential quadrature frequency shift keyed (DQFSK) acousticcommunication signal, eight sets of carrier frequencies to generate acombined FH and differential 8-frequency shift keyed (D8FSK) acousticcommunication signal, and/or M sets of carrier frequencies to generate acombined FH and differential M-frequency shift keyed (DMFSK) acousticcommunication signal.

A receiver, such as external computing device 108 or one or more sensorlink modules 602 attached to the skin of the body, decodes the acousticcommunication signal to recover the information signal. In particular,the receiver detects the carrier frequency from first set of carrierfrequencies f and/or the carrier frequency from second set of carrierfrequencies F. The receiver compares a detected carrier frequency to apreviously detected carrier frequency and assigns a recovered logicvalue based upon the similarity and/or difference between the detectedcarrier frequency and the previously detected carrier frequency. Thereceiver then assigns the recovered logic value to a recoveredinformation signal to recover the information signal.

To decode the acoustic communication signal encoded according to FIG.33C, the receiver may assign the first logic value to the recoveredinformation signal upon detecting the carrier frequency from first setof carrier frequencies f for time interval t_(AA), time interval t_(BB),and time interval t_(CC). Alternately, the receiver may assign the firstlogic value to the recovered information signal upon detecting thecarrier frequency from second set of carrier frequencies F for timeinterval t_(AA), time interval t_(BB), and time interval t_(CC).

The receiver may assign the second logic value to the recoveredinformation signal upon detecting the carrier frequency from first setof carrier frequencies f for time interval t_(AA) and time intervalt_(BB), then detecting the carrier frequency from second set of carrierfrequencies F for time interval t_(CC). Alternately, the receiver mayassign the second logic value to the recovered information signal upondetecting the carrier frequency from second set of carrier frequencies Ffor time interval t_(AA), time interval t_(BB), then detecting thecarrier frequency from first set of carrier frequencies f for timeinterval t_(CC).

The receiver may assign the third logic value to the recoveredinformation signal upon detecting the carrier frequency from second setof carrier frequencies F for time interval t_(AA) and time intervalt_(BB), then detecting the carrier frequency from first set of carrierfrequencies f for time interval t_(CC). Alternatively, the receiver mayassign the third logic value to the recovered information signal upondetecting the carrier frequency from first set of carrier frequencies ffor time interval t_(AA) and time interval t_(BB), then detecting thecarrier frequency from second set of carrier frequencies F for timeinterval t_(CC).

The receiver may assign the fourth logic value to the recoveredinformation signal upon detecting the carrier frequency from first setof carrier frequencies f for time interval t_(AA), the carrier frequencyfrom second set of carrier frequencies F for time interval t_(BB), thendetecting the carrier frequency from first set of carrier frequencies ffor time interval t_(CC). Alternatively, the receiver may assign thefourth logic value to the recovered information signal upon detectingthe carrier frequency from second set of carrier frequencies F for timeinterval t_(AA), the carrier frequency from first set of carrierfrequencies f for time interval t_(BB), then detecting the carrierfrequency from second set of carrier frequencies F for time intervalt_(CC). However, this example is not limiting, those skilled in the artwill recognize that the receiver may decode the acoustic communicationsignal to represent any suitable number of logic values by detecting anysuitable number of carrier frequencies from one or more sets of carrierfrequencies without departing from the spirit and scope of theinvention. For example, the receiver may decode the acousticcommunication signal using four sets of carrier frequencies to decodethe combined FH and DQFSK acoustic communication signal, eight sets ofcarrier frequencies to decode the combined FH and D8FSK acousticcommunication signal, and/or M sets of carrier frequencies to decode thecombined FH and DMFSK acoustic communication signal.

v. Combination of Frequency Hopping and Differential Frequency ShiftKeying, and Differential Phase Shift Keying

FIG. 34A illustrates a combined FH, DFSK, and DPSK scheme to encodeand/or decode an acoustic communication signal according to an exemplaryembodiment of the present invention. From the discussion of FIG. 27above, a transmitter, such as communications module 204, transmits anacoustic communication signal 3400, such as communication signal 106, byencoding an information signal, such as sensor output signal 212, ontofrequency channels ch₁ through ch_(N) corresponding to time intervals t₁through t_(N). From the discussion of FIG. 33A, frequency channels ch₁through ch_(N) may be assigned to a first set of carrier frequencies fincluding carrier frequencies f₁ through f_(M/2) and a second set ofcarrier frequencies F including carrier frequencies f_(M/2+1) throughf_(M/2). Referring back to FIG. 34A, the transmitter embeds one or morephases, denoted as ω₁ through ω_(i), of a corresponding carrierfrequency from first set of carrier frequencies f and/or one or morephases ω₁ through ω_(i) from second set of carrier frequencies F ontofrequency channels ch₁ through ch_(N) to encode the information signal.The transmitter embeds one or more phases ω₁ through ω_(i) correspondingto one or more sets of carrier frequencies onto each frequency channelin frequency channels ch₁ through ch_(N) to encode the informationsignal.

As shown in FIGS. 34B and 34C, the transmitter transmits a first phaseω₁ of a carrier frequency from first set of carrier frequencies f for atime interval t_(A) and a time interval t_(B) corresponding to a timeinterval t_(AA), and a time interval t_(A) and a time interval t_(B)corresponding to a time interval t_(BB) to represent a first logicvalue, such as a binary zero-zero-zero. A combination of time intervalt_(A) and time interval t_(B) is substantially less than or equal tocorresponding time interval t_(AA) and/or corresponding time intervalt_(BB). Time interval t_(AA) and time interval t_(BB) is substantiallyless than or equal to corresponding time intervals t₁ through t_(N) asdiscussed in FIG. 27.

A second logic value, such as a binary zero-zero-one, may be representedby transmitting the first phase ω₁ of the carrier frequency from firstset of carrier frequencies f for time interval t_(A) and time intervalt_(B) corresponding to time interval t_(AA), then the first phase ω₁ ofthe carrier frequency from first set of carrier frequencies f for timeinterval t_(A) followed by a second phase ω₂ of the carrier frequencyfrom first set of carrier frequencies f for time interval t_(B), timeinterval t_(A) and time interval t_(B) corresponding to time intervalt_(BB).

A third logic value, such as a binary zero-one-one, may be representedby transmitting the first phase ω₁ of the carrier frequency from firstset of carrier frequencies f for time interval t_(A) and time intervalt_(B) corresponding to time interval t_(AA) then a first phase ω₃ of thecarrier frequency from second set of carrier frequencies F for timeinterval t_(A) followed by a second phase ω₄ of the carrier frequencyfrom second set of carrier frequencies F for time interval t_(B), timeinterval t_(A) and time interval t_(B) corresponding to the timeinterval t_(BB).

A fourth logic value, such as binary zero-one-zero, may be representedby transmitting the first phase ω₁ of the carrier frequency from firstset of carrier frequencies f for time interval t_(A) and time intervalt_(B) corresponding to time interval t_(AA), then the first phase ω₃ ofthe carrier frequency from second set of carrier frequencies F for timeinterval t_(A) and time interval t_(B) corresponding to time intervalt_(BB).

A fifth logic value, such as binary one-zero-zero, may be represented bytransmitting the first phase ω₁ of the carrier frequency from first setof carrier frequencies f for time interval t_(A) followed by the secondphase ω₂ of the carrier frequency from first set of carrier frequenciesf for time interval t_(B), time interval t_(A) and time interval t_(B)corresponding to time interval t_(AA), then the second phase ω₂ of thecarrier frequency from first set of carrier frequencies f for timeinterval t_(A) and time interval t_(B) corresponding to time intervalt_(BB).

A sixth logic value, such as binary one-zero-one, may be represented bytransmitting the first phase ω₁ of the carrier frequency from first setof carrier frequencies f for time interval t_(A) followed by the secondphase ω₂ of the carrier frequency from first set of carrier frequenciesf for time interval t_(B), time interval t_(A) and time interval t_(B)corresponding to time interval t_(AA), then the second phase ω₂ of thecarrier frequency from first set of carrier frequencies f for timeinterval t_(A) followed by the by the second phase ω₂ of the carrierfrequency from first set of carrier frequencies f for time intervalt_(B), time interval t_(A) and time interval t_(B) corresponding to timeinterval t_(BB).

A seventh logic value, such as binary one-one-one, may be represented bytransmitting the first phase ω₁ of the carrier frequency from first setof carrier frequencies f for time interval t_(A) followed by the secondphase ω₂ of the carrier frequency from first set of carrier frequenciesf for time interval t_(B), time interval t_(A) and time interval t_(B)corresponding to time interval t_(AA), then the first phase ω₃ of thecarrier frequency from second set of carrier frequencies F for timeinterval t_(A) followed by the second phase ω₄ of the carrier frequencyfrom second set of carrier frequencies F for time interval t_(B), timeinterval t_(A) and time interval t_(B) corresponding to time intervalt_(BB).

An eighth logic value, such as binary one-one-zero, may be representedby transmitting the first phase ω₁ of the carrier frequency from firstset of carrier frequencies f for time interval t_(A) followed by thesecond phase ω₂ of the carrier frequency from first set of carrierfrequencies f for time interval t_(B), time interval t_(A) and timeinterval t_(B) corresponding to time interval t_(AA), then the firstphase ω₃ of the carrier frequency from second set of carrier frequenciesF for time interval t_(A) and time interval t_(B) corresponding to timeinterval t_(BB). However, this example is not limiting, those skilled inthe art will recognize that the transmitter may encode the informationsignal to represent any suitable number of logic values by transmittingany suitable number of carrier frequencies from one or more sets ofcarrier frequencies where each carrier frequency includes one or morephase ω₁ through ω_(i) without departing from the spirit and scope ofthe invention.

FIG. 35 illustrates a block diagram of a transmitter to encode aninformation signal to a combination of FH, DFSK and DPSK acousticcommunication signal according to an exemplary embodiment of the presentinvention. A transmitter 3500 may be used to generate an acousticcommunication signal 3552, such as communication signal 3400 as shown inFIG. 34A, based on an information signal 3550, such as sensor outputsignal 212. Transmitter 3500 may represent an exemplary embodiment ofcommunications module 204. As will be understood by persons skilled inthe relevant art from the teachings provided herein, transmitter 3500may be readily implemented in hardware, software, or a combination ofhardware and software. For example, based on the teachings providedherein, a person skilled in the relevant art could implement transmitter3500 via a combination of one or more application specific integratedcircuits and a processor core for implementing software commands storedin one or more attached memories. However, this example is not limiting,and other implementations are within the scope and spirit of the presentinvention.

As shown in FIG. 35, transmitter 3500 may include an acousticcommunications module 3502 and a radiating element 3504. Acousticcommunications module 3502 includes a bit splitter 3504, a multiplier3506, a delay module 3508, a carrier generator 3510, a DFSK switch 3512,a phase shifting module 3514, and a DPSK switch 3516. Acousticcommunications module 3502 may represent an exemplary embodiment ofacoustic communications module 302.

Bit splitter 3504 receives information signal 3550. Bit splitter 3504parses or partitions the information signal 3550 into a first datastream 3554A and a second data stream 3554B. Bit splitter 3504 maypartition information signal 3550 into one or more bits, one or morebytes, one or more symbols, or any other suitable manner that will beapparent to those skilled in the relevant art. First bit stream 3554Aand second bit stream 3554B may be of similar or of dissimilar lengths.

A multiplier 3506A compares first data stream 3554A to a first delayedDPSK switch control signal 3556A to produce a DPSK switch control signal3558A. A first delay module 3508A delays DPSK switch control signal3558A by one or more bits, one or more bytes, one or more symbols, orany other suitable manner based upon a data length of the DPSK switchcontrol signal 3558A to produce first delayed DPSK switch control signal3556A. In an exemplary embodiment, first delay module 3508A delays DPSKswitch control signal 3558A by one bit. Likewise, a multiplier 3506Bmultiplies second data stream 3554B and a second delayed encoded datastream 3556B to produce a second encoded data stream 3558B. A seconddelay module 3508B delays second encoded data stream 3558B by one ormore bits, one or more bytes, one or more symbols, or any other suitablemanner based upon a data length of the second encoded data stream 3558Bto produce second delayed encoded data stream 3558B. In an exemplaryembodiment, second delay module 3508B delays second encoded data stream3558B by one bit.

The carrier generator 3510 generates a first carrier frequency 3562Afrom a first set of carrier frequencies and a second carrier frequency3562B from a second set of carrier frequencies. More specifically,carrier generator 3510 generates one or more carrier frequencies, suchas carrier frequencies f₁ through f_(M) to provide an example, accordingto the FH scheme as discussed in conjunction with FIG. 27. Carriergenerator 3510 then divides the one or more carrier frequencies into thefirst set of carrier frequencies and the second set of carrierfrequencies as discussed in FIG. 33A.

The DFSK switch 3512 selects between first carrier frequency 3562A andsecond carrier frequency 3562B based upon second encoded data stream3558B to generate a DFSK data stream 3564. For example, DPSK switch 3516may select first carrier frequency 3562A when second encoded data stream3558B corresponds to a first logical value, such as a binary zero toprovide an example. Likewise, DPSK switch 3516 may select second carrierfrequency 3562B when second encoded data stream 3558B corresponds to asecond logical value, such as a binary one to provide an example.

Phase shifting module 3514 alters a phase of DFSK data stream 3564 toproduce a phase shifted DFSK data stream 3566. In an exemplaryembodiment, phase shifting module 3514 alters the phase of DFSK datastream 3564 by one hundred eighty degrees by inverting DFSK data stream3564. DPSK switch 3516 selects between DFSK data stream 3564 and phaseshifted DFSK data stream 3566 based upon first encoded data stream 3558Bto generate a combined DFSK and DPSK data stream 3568. For example, DPSKswitch 3516 may select phase shifted DFSK data stream 3566 when DPSKswitch control signal 3558A corresponds to a first logical value, suchas a binary zero to provide an example. Likewise, DPSK switch 3516 mayselect DFSK data stream 3564 when DPSK switch control signal 3558Acorresponds to a second logical value, such as a binary one to providean example.

Radiating element 3504 converts combined DFSK and DPSK data stream 3568to an acoustic representation to generate acoustic communication signal3552 based upon combined DFSK and DPSK data stream 3568. Radiatingelement 3504 may represent an exemplary embodiment of radiating element304. Radiating element 3504 may be, but is not limited to, anelectromechanical transducer or piezoelectric (e.g., PZT, PVDF, etc.)element or transducer that vibrates at acoustic frequencies.

FIG. 36 illustrates a block diagram of a receiver to decode aninformation signal from an acoustic communication signal encoded using acombination of FH, DFSK and DPSK according to an exemplary embodiment ofthe present invention. A receiver 3600, such as external computingdevice 108 or one or more sensor link modules 602 attached to the skinof the body, decodes an acoustic communication signal 3650 to recover aDFSK component 3652 and a DPSK component 3654. As shown in FIG. 36,receiver 3600 may include a radiating element 3602, a carrier generator3604, a DFSK/DPSK demodulator 3606, a DPSK switch 3608, and adifferential decoder 3610.

Radiating element 3602 receives acoustic communication signal 3650, suchas acoustic communication signal 3400 to provide an example. Radiatingelement 3602 converts acoustic communication signal 3650 to anelectrical signal to generate an electrical communication signal 3656.Radiating element 3602 may be, but is not limited to, anelectromechanical transducer or piezoelectric (e.g., PZT, PVDF, etc.)element or transducer that vibrates at acoustic frequencies.

Carrier generator 3604 generates a first carrier frequency 3658A from afirst set of carrier frequencies and a second carrier frequency 3658Bfrom a second set of carrier frequencies. More specifically, carriergenerator 3604 generates one or more carrier frequencies, such ascarrier frequencies f₁ through f_(M) to provide an example, according tothe FH scheme as discussed in conjunction with FIG. 27. Carriergenerator 3604 then divides the one or more carrier frequencies into thefirst set of carrier frequencies and the second set of carrierfrequencies as discussed in FIG. 33A.

DFSK/DPSK demodulator 3606 demodulates electrical communication signal3656 using a corresponding carrier frequency to produce a correspondingDFSK output 3660 and a corresponding DPSK output 3662. Morespecifically, DFSK/DPSK demodulator 3606A demodulates electricalcommunication signal 3656 using first carrier frequency 3658A from thefirst set of carrier frequencies to produce a DFSK output 3660A and aDPSK output 3662A. Likewise, DFSK/DPSK demodulator 3606B demodulateselectrical communication signal 3656 using second carrier frequency3658B from the second set of carrier frequencies to produce a DFSKoutput 3660B and a DPSK output 3662B.

FIG. 37 illustrates a block diagram of a demodulator to decode aninformation signal from an acoustic communication signal encoded using acombination of FH, DFSK, and DPSK according to an exemplary embodimentof the present invention. DFSK/DPSK demodulator 3700 is an exemplaryembodiment of DFSK/DPSK demodulator 3606A and/or DFSK/DPSK demodulator3606B as shown in FIG. 36.

Referring to FIG. 37, DFSK/DPSK demodulator 3700 operates uponelectrical communication signal 3656 using a corresponding carrierfrequency 3658 to produce a corresponding DFSK output 3660 and acorresponding DPSK output 3662. DFSK/DPSK demodulator 3700 includes amultiplier 3702, a phase shifter 3704, an integrator 3706, a multiplier3708, a delay module 3710, a summation network 3712, an in-phasecorrelator 3714, an in-phase correlator 3716, a decision device 3718, aquadrature phase correlator 3720, a quadrature phase correlator 3722,and a summation network 3724.

Multiplier 3702 downconverts electrical communication signal 3656 usinga corresponding carrier frequency to produce a correspondingdownconverted communication signal 3752. More specifically, a firstmultiplier 3702A downconverts electrical communication signal 3656 usingcarrier frequency 3658 to produce a first downconverted communicationsignal 3752A. Likewise, a second multiplier 3702B downconvertselectrical communication signal 3656 using a phase shifted carrierfrequency 3750 to produce a second downconverted communication signal3752B. Phase shifter 3704 delays or shifts a phase of carrier frequency3658 to produce phase shifted carrier frequency 3750. In an exemplaryembodiment, phase shifter 3704 shifts the phase of carrier frequency3658 by ninety degrees.

Integrator 3706 integrates a corresponding downconverted communicationsignal 3752. More specifically, integrator 3706A accumulates firstdownconverted communication signal 3752A within each half-symbolinterval of T/2 to produce an in-phase information signal 3754A.Likewise, integrator 3706B accumulates second downconvertedcommunication signal 3752B within each half-symbol interval of T/2 toproduce a quadrature phase information signal 3754B.

Multiplier 3708 multiplies in-phase information signal 3754A and/orquadrature phase information signal 3754B with a delayed in-phaseinformation signal 3756A and/or a delayed quadrature phase informationsignal 3756B. More specifically, multiplier 3708A multiplies in-phaseinformation signal 3754A with delayed in-phase information signal 3756Ato produce an in-phase decision statistic 3758A. Delay module 3710Adelays in-phase information signal 3754A by a half-symbol interval ofT/2 to produce delayed in-phase information signal 3756A. Likewise,multiplier 3708B multiplies quadrature phase information signal 3754Bwith delayed quadrature phase information signal 3756B to produce aquadrature phase decision statistic 3758B. Delay module 3710B delaysquadrature phase information signal 3754B by a half-symbol interval ofT/2 to produce delayed quadrature phase information signal 3756B.

Summation network 3712 combines in-phase decision statistic 3758A andin-phase decision statistic 3758A to produce a decision statistic 3760.Decision device 3718 assigns a logic value to DPSK output 3662 basedupon decision statistic 3760. In an exemplary embodiment, decisiondevice 3718 implements a signum function. For example, when decisionstatistic 3760 is less than zero, decision device 3718 assigns a firstbit estimate to DPSK output 3662. Likewise, when decision statistic 3760is greater than zero, decision device 3718 assigns a second bit estimateto DPSK output 3662.

In-phase correlator 3714 correlates in-phase information signal 3754A toproduce a correlated in-phase information signal 3762A. Likewise,in-phase correlator 3716 correlates delayed in-phase information signal3756A to produce a correlated delayed in-phase information signal 3762B.Quadrature phase correlator 3720 correlates quadrature informationsignal 3754B to produce a correlated quadrature information signal3764A. Likewise, quadrature correlator 3722 correlates delayedquadrature information signal 3756B to produce a correlated delayedin-phase information signal 3764B. Summation network 3724 then combinescorrelated in-phase information signal 3762A, correlated delayedin-phase information signal 3762B, correlated quadrature informationsignal 3764A, and correlated delayed in-phase information signal 3764Bto produce DFSK output 3660.

FIG. 38 illustrates a block diagram of a demodulator to decode aninformation signal from an acoustic communication signal encoded using acombination of FH, DFSK, and DPSK according to another exemplaryembodiment of the present invention. DFSK/DPSK demodulator 3800 is anexemplary embodiment of DFSK/DPSK demodulator 3606A and/or DFSK/DPSKdemodulator 3606B as shown in FIG. 36.

Referring to FIG. 38, DFSK/DPSK demodulator 3800 operates uponelectrical communication signal 3656 using a corresponding carrierfrequency 3658 to produce a corresponding DFSK output 3660 and acorresponding DPSK output 3662. DFSK/DPSK demodulator 3800 includes amultiplier 3802, a phase shifter 3804, an integrator 3806, a multiplier3808, a delay module 3810, a multiplier 3812, a summation network 3814,a difference network 3816, a decision device 3818, a decision device3820, a bit combiner 3822, an in-phase correlator 3824, an in-phasecorrelator 3826, a quadrature phase correlator 3828, a quadrature phasecorrelator 3830, and a summation network 3832. Multiplier 3802downconverts electrical communication signal 3656 using a correspondingcarrier frequency to produce a corresponding downconverted communicationsignal 3852. More specifically, a first multiplier 3802A downconvertselectrical communication signal 3656 using carrier frequency 3658 toproduce a first downconverted communication signal 3852A. Likewise, asecond multiplier 3802B downconverts electrical communication signal3656 using a phase shifted carrier frequency 3850 to produce a seconddownconverted communication signal 3852B. Phase shifter 3804 delays orshifts a phase of carrier frequency 3658 to produce phase shiftedcarrier frequency 3850. In an exemplary embodiment, phase shifter 3804shifts the phase of carrier frequency 3658 by ninety degrees.

Integrator 3806 integrates a corresponding downconverted communicationsignal 3852. More specifically, integrator 3806A accumulates firstdownconverted communication signal 3852A within each half-symbolinterval of T/2 to produce an in-phase information signal 3854A.Likewise, integrator 3806B accumulates second downconvertedcommunication signal 3852B within each half-symbol interval of T/2 toproduce a quadrature phase information signal 3854B.

Multiplier 3808 multiplies in-phase information signal 3854A and/orquadrature phase information signal 3854B with a delayed in-phaseinformation signal 3856A and/or a delayed quadrature phase informationsignal 3856B. More specifically, multiplier 3808A multiplies in-phaseinformation signal 3854A with delayed in-phase information signal 3856Ato produce an in-phase decision statistic 3858A. Delay module 3810Adelays in-phase information signal 3854A by a half-symbol interval ofT/2 to produce delayed in-phase information signal 3856A. Likewise,multiplier 3808B multiplies quadrature phase information signal 3854Bwith delayed quadrature phase information signal 3856B to produce aquadrature phase decision statistic 3858B. Delay module 3810B delaysquadrature phase information signal 3854B by a half-symbol interval ofT/2 to produce delayed quadrature phase information signal 3856B.

Multiplier 3828A multiplies in-phase phase information signal 3854A withquadrature phase information signal 3854B to produce a decisionstatistic 3860A. Likewise, multiplier 3828B multiplies in-phase phaseinformation signal 3854B with quadrature phase information signal 3854Bto produce a decision statistic 3860B.

Summation network 3814 combines in-phase decision statistic 3858A andin-phase decision statistic 3858A to produce a decision statistic 3862.Likewise, difference network 3816 subtracts decision statistic 3860A anddecision statistic 3860B to produce a decision statistic 3864. Decisiondevice 3818 assigns a logic value to a first DPSK output 3866 based upondecision statistic 3862. In an exemplary embodiment, decision device3818 implements a signum function. For example, when decision statistic3862 is less than zero, decision device 3818 assigns a first bitestimate to first DPSK output 3866. Likewise, when decision statistic3860 is greater than zero, decision device 3818 assigns a second bitestimate to first DPSK output 3866. Similarly, decision device 3820assigns a logic value to a second DPSK output 3868 based upon decisionstatistic 3862. In an exemplary embodiment, decision device 3820implements a signum function. For example, when decision statistic 3862is less than zero, decision device 3820 assigns a first bit estimate tothe second DPSK output 3868. Likewise, when decision statistic 3860 isgreater than zero, decision device 3820 assigns a second bit estimate tosecond DPSK output 3868. Bit combiner 3822 combines first DPSK output3868 and second DPSK output 3868 to produce DPSK output 3662A.

In-phase correlator 3824 correlates delayed in-phase information signal3856A to produce a correlated delayed in-phase information signal 3870A.Likewise, in-phase correlator 3826 correlates in-phase informationsignal 3854A to produce a correlated in-phase information signal 3870B.Quadrature phase correlator 3828 correlates quadrature informationsignal 3854B to produce a correlated quadrature information signal3872A. Likewise, quadrature correlator 3830 correlates delayedquadrature information signal 3856B to produce a correlated delayedin-phase information signal 3872B. Summation network 3832 then combinescorrelated in-phase information signal 3870A, correlated delayedin-phase information signal 3870B, correlated quadrature informationsignal 3872A, and correlated delayed in-phase information signal 3872Bto produce DFSK output 3660.

Referring back to FIG. 36, differential decoder 3610 produces DFSKcomponent 3652 based upon DFSK output 3660A and DFSK output 3660B. In anexemplary embodiment, differential decoder 3610 assigns a first logicvalue, such as a binary zero, to DFSK component 3652 when thecombination of DFSK output 3660A and DFSK output 3660B is substantiallyequal to zero. Otherwise, differential decoder 3610 assigns a secondlogic value, such as a binary one, to DFSK component 3652 when thecombination of DFSK output 3660A and DFSK output 3660B is substantiallyequal to one. In addition, differential decoder 3610 produces a DPSKselection signal 3670.

DPSK switch 3608 selects DPSK output 3662A or DPSK output 3662B basedupon DPSK selection signal 3670 to produce DPSK component 3654. Forexample, DPSK switch 3608 selects DPSK output 3662A when DPSK selectionsignal 3670 corresponds to a first logic value, such as a binary zero.Likewise, DPSK switch 3608 selects DPSK output 3662B when DPSK selectionsignal 3670 corresponds to a second logic value, such as a binary one.

vi. Use of Multiple Frequency Bands with a Combination of FrequencyHopping and Time Interval Encoding

FIG. 39A illustrates a hopping pattern used to encode and/or decode anacoustic communication signal using multiple frequency bands with FHaccording to an exemplary embodiment of the present invention. As shownin FIG. 39A, an available bandwidth of the communication channel issubstantially equally divided into three frequency bands B₁ through B₃.For example, as shown in FIG. 39A, frequency band B₁ includes a firstbandwidth encompassing carrier frequencies f₁ through f_(i), frequencyband B₂ includes a second bandwidth encompassing carrier frequenciesf₁₊₁ through f_(M−i−1), and frequency band B₃ includes a third bandwidthencompassing carrier frequencies f_(M−i) through f_(M). However, thisexample is not limiting, the available bandwidth of the communicationchannel may be divided into one or more frequency bands B₁ throughB_(K). In addition, the available bandwidth of the communication channelneed not be substantially equally divided into one or more frequencybands B₁ through B_(K). For example, frequency band B₁ may encompass agreater amount of the available bandwidth of the communication channelwhen compared to frequency band B₂.

In an embodiment utilizing substantially different frequency bands B₁and B₂, a received amplitude of a particular first frequency in band B₁as compared with a received amplitude of a particular second frequencyin band B₂ can derive distance from a sensor device 104 to a receiversuch as sensor link 602. Acoustic attenuation of signals is proportionalto a frequency of transmission for a given medium, such as with humanbody 102. However, the knowledge of absolute amplitude of emission isnot easily attainable for a reference to calculate a distance from aresulting attenuation. Considering multiple frequencies with multipleamplitudes, a sensitive receiver may be able to calculate with accuracya difference between received amplitudes of these two frequencies. Amathematical model with known quantities of attenuation versus distancefor both frequencies may then also solve a difference of knownattenuations versus distances for both frequencies. In such an example,there is only one final solution that resolves the distance from a matchof amplitude differentials with the difference in amplitude actuallyreceived. In so doing, use of a single phased array receiver (for thedirection component of the location) in combination with use of multiplefrequency bands (for the distance component of the location) canpotentially resolve the location of the origin of acoustic signals to areasonable accuracy.

Referring back to FIG. 39A, a pulse P₁ through P_(N) may be assigned acorresponding carrier frequency from one or more frequency bands B₁through B_(K). For example, pulse P₁ may be assigned to carrierfrequency f₁ from frequency band B₁, carrier frequency f_(i+1) fromfrequency band B₂, and/or carrier frequency f_(M−i) from frequency bandB₃. However, this example is not limiting, those skilled in the artswill recognize that pulses P₁ through P_(N) may be assigned to one ormore frequency bands B₁ through B_(K) using any other suitable sequenceof carrier frequencies f₁ through f_(M) without departing from thespirit and scope of the invention. In an exemplary embodiment, one ormore pulses P₁ through P_(N) are sequentially assigned to the carrierfrequencies. After transmission and/or reception of pulse P₁ using acarrier frequency from one of frequency bands B₁ through B₃, atransmitter and/or a receiver sequentially reassigns the carrierfrequency associated with the frequency band according to the hoppingscheme. For example, if pulse P₁ is transmitted and/or received usingcarrier frequency f₁ associated with frequency band B₁, the transmitterand/or a receiver reassigns frequency band B₁ to a next carrierfrequency according to the hopping scheme and leaves frequency bands B₂and B₃ in their current state.

FIG. 39B illustrates a multiple frequency band with FH scheme to encodeand/or decode an acoustic communication signal according to an exemplaryembodiment of the present invention. A transmitter, such ascommunications module 204, transmits an acoustic communication signal,such as communication signal 106, by encoding an information signal,such as sensor output signal 212, using one or more pulses P₁ throughP_(N) as described in FIG. 39A.

The transmitter selects one or more pulses P₁ through P_(N) fromfrequency bandwidths B₁ through B₃ to encode the information signal. Asshown in FIG. 39B, the transmitter transmits a first pulse, such aspulse P₁, assigned to a carrier frequency from frequency band B₁ for atime interval t_(AA) and a time interval t_(BB) followed by a thirdpulse, such as pulse P₃, assigned to a carrier frequency from frequencyband B₃ for time interval t_(CC) to represent a first logic value, suchas a binary zero-zero. Time interval t_(AA), time interval t_(BB), andtime interval t_(CC) are greater than or equal to a duration of acorresponding pulse in one or more pulses P₁ through P_(N). In anexemplary embodiment, third pulse P₃ indicates an end of a transmission.However, this example is not limiting, those skilled in the arts willrecognize that any one of pulses P₁ through P_(N) may be used toindicate the end of the transmission without departing from the spiritand scope of the invention.

A second logic value, such as a binary zero-one, may be represented bytransmitting the first pulse assigned to the carrier frequency fromfrequency band B₁ for time interval t_(AA), a second pulse, such aspulse P₂, assigned to a carrier frequency from frequency band B₂ fortime interval t_(BB), and third pulse P₃ assigned to a carrier frequencyfrom frequency band B₃ for time interval t_(CC) to indicate the end oftransmission.

A third logic value, such as a binary one-one, may be represented bytransmitting the pulse assigned to the carrier frequency from frequencyband B₂ for time interval t_(AA) and time interval t_(BB), followed bythe third pulse assigned to a carrier frequency from frequency band B₃for time interval t_(CC) to indicate the end of transmission.

A fourth logic value, such as a binary one-zero, may be represented bytransmitting the pulse assigned to the carrier frequency from frequencyband B₂ for time interval t_(AA), a pulse assigned to the carrierfrequency from frequency band B₁ for time interval t_(BB), followed bythe third pulse assigned to the carrier frequency from frequency band B₃for time interval t_(CC). However, this example is not limiting, anylogic value may be represented by transmitting pulses P₁ through P_(N)assigned to carrier frequencies from frequency bands B₁ through B_(K).For example, a binary zero-zero-zero-one-zero-one-one-zero may berepresented by transmitting the first pulse, the second pulse, and thethird pulse assigned to a carrier frequency from frequency band B₁, afourth pulse assigned to a carrier frequency from frequency band B₂, afifth pulse assigned to a carrier frequency from frequency band B₁, asixth and a seventh pulse assigned to a carrier frequency from frequencyband B₂, and an eighth pulse assigned to a carrier frequency fromfrequency band B₁, followed by a ninth pulse assigned to a carrierfrequency from frequency band B₃ to indicate the end of transmission.

A receiver, such as external computing device 108 or one or more sensorlink modules 602 attached to the skin of the body, decodes the acousticcommunication signal to recover the information signal. The receiverassigns the recovered logic value by detecting the carrier frequencyfrom frequency band B₁, and/or the carrier frequency from frequency bandB₂ until the end of transmission as indicated by detecting the carrierfrequency from frequency band B₃. In an exemplary embodiment, thereceiver includes three detection circuits, one detection circuit foreach frequency band B₁ through B₃.

To decode the acoustic communication signal encoded according to FIG.39B, the receiver may assign the first logic value to a recoveredinformation signal by detecting first pulse P₁ assigned to the carrierfrequency from frequency band B₁ for a time interval t_(AA) and a timeinterval t_(BB) followed by third pulse P₃ assigned to the carrierfrequency from frequency band B₃ for time interval t_(CC) to indicatethe end of transmission.

The receiver may assign the second logic value to the recoveredinformation signal by detecting first pulse P₁ assigned to the carrierfrequency from frequency band B₁ for time interval t_(AA), second pulseP₂ assigned to the carrier frequency from frequency band B₂ for timeinterval t_(BB), followed by third pulse P₃ assigned to the carrierfrequency from frequency band B₃ for time interval t_(CC) to indicatethe end of transmission.

The receiver may assign the third logic value to the recoveredinformation signal by detecting pulse P₂ assigned to the carrierfrequency from frequency band B₂ for time interval t_(AA) and timeinterval t_(BB), followed by third pulse P₃ assigned to the carrierfrequency from frequency band B₃ for time interval t_(CC) to indicatethe end of transmission.

The receiver may assign the fourth logic value to the recoveredinformation signal by detecting pulse P₂ assigned to the carrierfrequency from frequency band B₂ for time interval t_(AA), first pulseP₁ assigned to the carrier frequency from frequency band B₁ for timeinterval t_(BB), followed by a third pulse P₃ assigned to the carrierfrequency from frequency band B₃ for time interval t_(CC) to indicatethe end of transmission. However, this example is not limiting, anylogic value may be represented by transmitting pulses P₁ through P_(N)for any suitable number of time intervals. For example, the receiver mayassign a binary zero-zero-zero-one-zero-one-one-zero to the recoveredinformation signal by detecting the first pulse, the second pulse, andthe third pulse assigned to a carrier frequency from frequency band B₁,a fourth pulse assigned to a carrier frequency from frequency band B₂, afifth pulse assigned to a carrier frequency from frequency band B₁, asixth and a seventh pulse assigned to a carrier frequency from frequencyband B₂, and an eighth pulse assigned to a carrier frequency fromfrequency band B₁ followed by a ninth pulse assigned to a carrierfrequency from frequency band B₃ to indicate the end of transmission.

FIG. 39C illustrates a multiple frequency band with FH and time intervalencoding scheme to encode and/or decode an acoustic communication signalaccording to an exemplary embodiment of the present invention. As shownin FIG. 39C, a corresponding time delay T₁ through T_(N) having one ormore time delay intervals, denoted as τ_(N), may be used to implement arepeat function. The duration of time delay interval τ_(N) issubstantially less than or equal to the duration of a correspondingpulse in one or more pulses P₁ through P_(N). The repeat functionindicates that the next bits of the acoustic communication signal aresubstantially equal to a previous bit transmitted and/or received basedupon a number of time delay intervals τ_(N). More specifically, delayingby a time delay interval τ_(N) after a binary one indicates that thenext bits in the acoustic communication signal also indicate a binaryone. Likewise, delaying by two time delay intervals τ_(N) after a binaryone indicates that the two next bits in the acoustic communicationsignal also indicate a binary one. For example, the repeat functionallows an eight bit word represented by binaryzero-one-one-one-one-one-one-one to be encoded and/or decoded bytransmitting and/or receiving a first pulse assigned to a carrierfrequency from frequency band B₁, a second pulse assigned to a carrierfrequency from frequency band B₂, and a period of five time delayintervals N, followed by a third pulse assigned to a carrier frequencyfrom frequency band B₃ to indicate the end of transmission.

The repeat function may also allow for the repetition of one or morebits, one or more bytes, one or more symbols, or any other suitable datalength or combination of data lengths. For example, the repeat functionmay also allow the eight bit word represented by binaryzero-one-one-one-one-one-one-one to be repeated n times by transmittingand/or receiving a first pulse assigned to a carrier frequency fromfrequency band B₁, a second pulse assigned to a carrier frequency fromfrequency band B₂, a period of five time delay intervals τ_(N), a thirdpulse assigned to a carrier frequency from frequency band B₃, a periodof n delay intervals τ_(N), followed by a fourth pulse assigned to acarrier frequency from frequency band B₃ to indicate the end oftransmission.

In another exemplary embodiment, the pulse assigned to a carrierfrequency from frequency band B₃ may be used to implement a truncationfunction. The truncation function indicates that the remaining bits ofthe acoustic communication signal are substantially equal to a previousbit transmitted and/or received. More specifically, truncating after abinary one indicates that the rest of the bits in the acousticcommunication signal are also binary one. Likewise, truncating after abinary zero indicates that the rest of the bits in the acousticcommunication signal are also binary zero. For example, the truncationfunction allows an eight bit word represented by binaryzero-one-one-one-one-one-one-one to be encoded and/or decoded usingsubstantially similar encoding and/or decoding as the second logic valueas discussed above. In this example, third pulse P₃ assigned to acarrier frequency from frequency band B₃ indicates that the remainingsix bits of the eight bit word are equal to a previous bit transmittedand/or received. Likewise, the truncation function allows an eight bitword represented by binary one-zero-zero-zero-zero-zero-zero-zero to beencoded and/or decoded using substantially similar encoding and/ordecoding as the fourth logic value as discussed above. However, theseexamples are not limiting, the truncation function may be used toindicate that any suitable number of bits are substantially equal to theprevious bit transmitted and/or received. In addition, the transmitterand/or the receiver may use the truncation function in any locationthroughout the encoding and/or decoding of the acoustic communicationsignal.

In a further exemplary embodiment, the corresponding time delays T₁through T_(N), including one or more time delay intervals τ_(N), may beadditionally used to encode the acoustic communication signal. In thisexemplary embodiment, the transmitter transmits a first pulse assignedto a carrier frequency from one of the frequency bands, such as pulse P₁assigned to a carrier frequency from frequency band B₁, for a firstinterval of time, such as time interval t₁. The transmitter then waitsor ceases to transmit for a corresponding time delay, such as time delayT₁, before beginning the transmission of a second pulse assigned to acarrier frequency from one of the frequency bands, such as pulse P₂including a carrier frequency from frequency band B₂. The transmitterencodes the information signal by varying a length of the correspondingtime delay. More specifically, the transmitter encodes the informationsignal by delaying the transmission of the pulse by one or more timedelay intervals τ_(N). The one or more time delay intervals τ_(N) withina corresponding time delay T₁ through T_(N) represent a logic value. Thelogic value may be one or more bits, one or more bytes, one or moresymbols, or any other suitable data length or combination of datalengths. An individual delay interval in one or more time delayintervals τ_(N) may be a duration of one or more bits, one or morebytes, one or more symbols, or any other suitable data length orcombination of data lengths so long as the duration of an individualdelay interval τ_(N) is substantially less than or equal to the durationof a corresponding pulse in one or more pulses P₁ through P_(N).

In an additional exemplary embodiment, a pulse assigned to a carrierfrequency from one of the frequency bands transmitted and/or receivedprior to one or more time delay intervals τ_(N) may be used to implementan advancement function. In other words, the pulse assigned to thecarrier frequency from one of the frequency bands transmitted and/orreceived prior to one or more time delay intervals τ_(N) may correspondto a number of one or more time delay intervals τ_(N). In other words,the transmitter and/or the receiver supplements a transmitted and/or areceived one or more time delay intervals τ_(N) with a predeterminednumber of the one or more time delay intervals τ_(N).

As shown in FIG. 39D, a first pulse assigned to a carrier frequency froma first frequency band, such as pulse P₁ assigned to a carrier frequencyfrom frequency band B₁, may be assigned a value of zero delay intervalsτ_(N). Likewise, a second pulse assigned to a carrier frequency from asecond frequency band, such as pulse P₂ assigned to a carrier frequencyfrom frequency band B₂, may be assigned a value of i delay intervalsτ_(N). Finally, a n^(th) pulse assigned to a carrier frequency from an^(th) frequency band, such as pulse P_(N) assigned to a carrierfrequency from frequency band B_(N), may be assigned a value of j delayintervals τ_(N). However, this example is not limiting, one or morepulses P₁ through P_(N) may be assigned to any suitable value of delayintervals τ_(N) without departing from the spirit and scope of thepresent invention.

When encoding and/or decoding the acoustic communication signal, thetransmitter and/or the receiver encodes and/or decodes the acousticcommunication signal based upon an amount of one or more time delayintervals τ_(N) included within the acoustic communication signal. Onthe other hand, the transmitter and/or the receiver supplements thetransmitted and/or the received one or more time delay intervals τ_(N)by factoring in an additional i delay intervals τ_(N) when the pulseassigned to a carrier frequency from one of the frequency bandstransmitted and/or received prior to one or more time delay intervalsτ_(N) corresponds to the second pulse assigned to a carrier frequencyfrom the second frequency band. In other words, transmitting and/orreceiving the second pulse assigned to the carrier frequency from thesecond frequency band and waiting and/or measuring m time delayintervals τ_(N) is substantially identical to waiting and/or measuringm+i time delay intervals τ_(N) for the purposes of encoding and/ordecoding the acoustic communication signal. Likewise, the transmitterand/or the receiver supplements the transmitted and/or the received oneor more time delay intervals τ_(N) by factoring in an additional j delayintervals τ_(N) when the pulse assigned to a carrier frequency from oneof the frequency bands transmitted and/or received prior to the one ormore time delay intervals τ_(N) corresponds to the n^(th) pulse assignedto a carrier frequency from the n^(th) frequency band. In other words,transmitting and/or receiving the n^(th) pulse assigned to the carrierfrequency from the second frequency band and waiting and/or measuring mtime delay intervals τ_(N) is substantially identical to waiting and/ormeasuring m+j time delay intervals τ_(N) for the purposes of encodingand/or decoding the acoustic communication signal.

VII. Conclusion

While various embodiments of the present invention have been describedabove, it should be understood that they have been presented by way ofexample only, and not limitation. It will be apparent to persons skilledin the relevant art that various changes in form and detail can be madetherein without departing from the spirit and scope of the invention.For example, acoustic data communication schemes can be conceived thatcombine all the techniques above. Thus, the breadth and scope of thepresent invention should not be limited by any of the above-describedexemplary embodiments, but should be defined only in accordance with thefollowing claims and their equivalents.

What is claimed is:
 1. A method of communicating with an ingestiblecapsule, comprising: detecting a location of the ingestible capsule;focusing a multi-sensor acoustic array on the ingestible capsule; andcommunicating an acoustic information exchange with the ingestiblecapsule via the multi-sensor acoustic array; wherein detecting thelocation comprises: receiving an acoustic signal from the ingestiblecapsule; determining a respective phase delay for each sensor in themulti-sensor array that produces a maximum gain of the acoustic signal;adjusting a phase for each sensor in the multi-sensor array using thedetermined respective phase delay of the sensor in the multi-sensorarray; and deriving the location of the ingestible capsule from thedetermined phase delays.
 2. The method of claim 1, wherein thecommunicating step comprises at least one of: transmitting, via themulti-sensor acoustic array, the acoustic information exchange to theingestible capsule; and receiving, via the multi-sensor acoustic array,the acoustic information exchange from the ingestible capsule.
 3. Themethod of claim 1, wherein adjusting the phase delay comprises: changingthe phase delay by a given amount; measuring an amplitude of theacoustic signal; and repeating the changing and measuring steps untilthe amplitude of the acoustic signal is maximized.
 4. The method ofclaim 1, wherein adjusting the phase delay comprises: detecting thephase of the acoustic signal; and adjusting the phase delay of eachsensor until the signals received by each sensor are coherent.
 5. Themethod of claim 1, wherein detecting the location further comprises:determining the location of the ingestible capsule through a successiveapproximation.
 6. The method of claim 5, wherein determining thelocation further comprises: determining the location of the ingestiblecapsule using a previously known location as a starting point for thesuccessive approximation.
 7. The method of claim 1, whereincommunicating occurs periodically, continuously, or based on a givenevent.
 8. The method of claim 1, wherein deriving the location of theingestible capsule further comprises: identifying an angular directionof the ingestible capsule from the multi-sensor acoustic array based onphase separations of the acoustic signal between each sensor in themulti-sensor acoustic array; and identifying a distance to theingestible capsule from the multi-sensor acoustic array based ondifferences in time of arrival of the acoustic signal between eachsensor in the multi-sensor acoustic array.
 9. The method of claim 1,wherein each sensor in the multi-sensor array is a transducer, andwherein communicating comprises: implementing the phase delay for eachsensor in the multi-sensor array into a transmission signal to produce aphase-delayed signal; routing the phase-delayed signal to respectivetransducers in the multi-sensor array; and transmitting thephase-delayed signal from each transducer in the multi-sensor array tothe ingestible capsule.